My '90 Westy, with 123k miles, is going = in soon to have the leaking head gaskets replaced. Is there anything else they = should look at or do while it's there? Specifically, a valve job? It runs fine, gets = 19mpg around town and about 22 on the highway. The O2 sensor has never been = replaced. I guess I fall somewhere between regular maintenance and "if it ain't = broke, don't fix it".