some things to check-

-is the coolant oily?
-is the oil cap 'milky'?
-do you see white smoke from the tailpipe?

the bubbles in the coolant might or might not be a head gasket issue. perhaps the cooling system has an air leak (loose clamp or pinhole somewhere)

at this point, i would not condemn the head gasket.

even if it is, it is not that difficult to replace.

__________________
Ben
1987 190d 2.5Turbo