IMHO, after running 285K miles, this engine will need an overhaul before
next winter. The minimum compression is 15 BAR (218 psi) vs. 22 - 24 BAR
specification when new or overhauled.
The head gasket is probably OK but the piston rings are worn. It won't
just quit on you but will begin to use oil and be harder to start, even
when the weather is warm.