Do I really need to replace head gasket? on 2008 BMW 128i

I have a 1972 BMW model 2002, not the tii,your system didn't have my year and make. Compression 140 on all 4, there is white residue on spark plugs. Mechanic says I need to replace head gasket.What's your take on these symptoms? What is the average cost of head gasket replacement? What do you think of the Product "Steel Seal" instead of replacing the gasket? Thank you very much for your knowledge and help. Respectfully, Phoenix

Asked by for the 2008 BMW 128i
If the head gasket is leaking, the only good option is to replace it, don't use any "quick fix" products, they wont work.
A leaking head gasket can be verified by the presence of hydrocarbons in the cooling system. Here is some info: