if the coolant in the the sump... then as you rightly say it can get there via numerouse routes
cracked head or block would be worst case scenario. so you don't want to worry about that yet
check around the inlet manifold does it have water passages? i'm not familiar with big block V8, i,e did it leak at its inlet gasket and pour water into the sump via the valley, usually while cooling down.... if so its a set of inlet manifold gaskets and associated valley tray bits n bobs.. there will be tips and tricks for fitting this lot back that i don't know V8 person will be needed
rest the inlet in the valley with no gaskets to check fit and angles....
some of the studs for the timing cover and woter pump may go into the water jacket did one come out like a bolt...? or are they bolts with no sealer on?
re install with a few threads worth of sealer or loktite
if all good on the inlet and cover side of things
it is next most likley a head gasket problem between a water gallery and a combustion chamber.
pressure in the cooling system, once the engine is stopped, pushes water into the chamber and the water runs down into the crank case. you don't necesarily see much when motor is running becasue it vapourises instantly.
look for one cylinder that is particularly grotty, it might just be full of grot or it may look kinda varnished, it will look different to the rest , you may see little sign of a problem with the gasket depends on type and how much it glues itself to the block
check each head combsution chamber deck face and into the ports for signs of leakage i.e cracks or corroision holes
look for cracks between valve seats i.e running from exhaust to inlet or from 1 to plug thread in the top of the chamber
hopefully you see nothing
clean the block faces with plastic scrubbers try to avoid getting any of the gunk stuck down the cylinders . block off wter and oil galleries with some kind of stoppers... I could fit grub screws into the water passage and i used rubber end cap from a reel of cable for oil. dont loose them down the hole and remeber to take them out.
Rotate a piston to the top clean that area then move it down slightly and get a microfibre cloth in there to get the bits out. granted they will burn.. but you don't want them clagging up the rings
wipe surfaces down with brake cleaner or similar
decison time
you don't know why the gasket leaked if it was a heat or over heating issue in the past there is no guarantee that the head is flat. like a warped record its not going back...and the warp will vary based on tempertaure.
it might be worth taking both heads for the lightest skim to clean up the faces in theory this will be a matter of a few thou, but it will give you a clean face to work with with the correct level of surface roughness to work nice with a standard gasket . that surface won't be correct for a cometic shim gasket or copper both need surfaces ground to a specic smoothness.
This small skim in theory should not cause an issue with the inlet manifold mounting faces. which as you see are at an angle, the skim lowers the head and narrows the wedge shaped space you put the inlet manifold into.. just couple thou and a graphite inlet gasket should be ok any more and there is an equation somewhere that links the amount removed from the heads to the amount you need to remove from the inlet manifold face to get it to fit, avoids a chunk of trigonometry....
i used expanded graphite inlet and exhaust gaskets becasue i like them and i have never had a problem.... they are thick and compliant, they work well on mine that shares a gasket betwen exhaust and inlet allowing 3 different bits of flange all to mount leak free to the same flat surface, if they work here they will work anywhere, the standard gasket is metal shim fine on day one, easy to bugger up, on day 9000, with mis matched parts.
next is probably going to cause contention and lots will disagree
i fill with water only and the correct amount of K-seal, read the bottle
i run the engine up to temperature and drive it for a few 100 miles
if all good i dump the K seal/water, you don't want it hanging about if there is no emergency, re torque the head bolts (even on a monotorque gasket)
and fill with standard blue coolant
coolant is wetter than pure water, coolant will find a way out easier than water, and coolant can mess with gasket seal, hence i suggest water to start with while the gasket bakes...
many will say never ever ever ever ever put K-seal near an engine
professional builders don't, they have confidence in their ability to do a head gasket correctly and they did 4 yesturday will be doing 4 today and another six tomorrow..... no probs
the only people who do are backyard mechanics (i.e you and me) and the odd chap who is doing some re use of a cometic or copper gasket in an emrgency
you are not supposed to re use any head gasket !!!
copper can be re used if softened again, cometic steel shim style gasket is supposed be 1 use only, but pleanty re use them if the coating is still good or they bodge it with spray hylomar or copper coat spray on each side of each part of the shim pack...
you will be using standard head gasket... you can't bodge them back on.... so you need new ones every time, and as such making it work every time is key.....you don't wanner be doing this again in 3 weeks time, hence my suggestion
copper is probably overkill unles you are running some kind of monster motor with high cylinder pressures some kind of race machine or forced induction. read up about copper gaskets before use. handy also for correcting things you can get fat and thin versions to set CR and cater for strange piston crown/deck height combos.
K seal is not a good fix for a permanent leak but i see little impact of using it once for a short period of time to avoid a leak.....
if you still have a problem after all of this its time to take it to bits and get it checked by somone who knows what to look for, or indeed crack tested, penetrant dye checking sonic checking or pressure tested for the heads.
both expenive its a last resort kinda thing.
worst case its a tiny corrosion or casting flaw hole in a cylinder wall low down if it was near the top the radiator hose would have come off by itself...
Dave