My engine over heated getting home. Got the car home and hissing sound from under hood. When I opened hood, noticed steam hissing out from the coolant overflow container (overflow) tube. Nothing from any of the radiator pipes. Was at night and figured out there's nothing I could do.

Next morning I noticed a puddle of oily liquid under the car... a fairly big puddle. Looking into the coolant overflow container I could see a light brown creamy fudge way over the "max" line. Looks like oil is getting into the cooling system, and sign of maybe a blown head gasket, cracked head or cylinder block, or internal damage to water/oil galleries?

Checked the oil level and oil. Oil level was bet. Low and high, oil looked OK (not light brown cream like in coolant overflow tank. The car (3-cylinder 1992 charade) is not worth spending a lot of repair $ fixing so I'm trying one of those block sealer things you add to the radiator. Bought a product called "cargo metallic seal-up" which claims to seal cracks permanently in blocks, heads, head gaskets. The product claims...
"Seal-Up will easily repair holes of up to 1mm diameter and cracks of any length up to 0.5mm wide (both ofol which would result in major coolant loss). "
My question is I don't have any coolant loss but a "coolant" gain (over max mark in overflow tank of the light brown creamy mess). Oil is getting INTO the cooling system but NOT coolant into the engine. So will this product work for me? My thinking is the sealant will not be sucked into any engine cracks to fill in the cracks since oil is pushing into the cooling system. It would work if coolant was sucked into the engine. I'm not looking for a permanent fix but something that would give me a few more months life out of the car. Do you think a block sealer like seal-up (or similar product) would work? Would appreciate any comments.
Tia.