I have a 1991 535i with 160,000 miles. I've had it about 7 years now (bought it at 80,000 miles).
The water pump failed and it overheated 3 1/2 years ago. 6 months after that, I had to replace the cylinder head gasket. The cylinder head was sent to a machine shop to be checked out, and it checked out fine, no planing or resurfacing was needed.
Now, 3 years later, I'm all of a sudden losing coolant every 3 weeks and I've got oil in the coolant reservoir. I took it in to the shop, they flushed it, cleaned out the reservoir, and put in some Prestone coolant system sealant in order to avoid a cylinder head repair.
Well, two days later, the coolant is low again and the reservoir has frothy brown oil in it.
The shop says it probably needs a new cylinder head, since the gasket should have lasted more than three years (I haven't had any coolant system issues since the gasket was replaced).
My question: Do I go ahead and replace the cylinder head and expect to get another 100,000 miles out of this 535i, or do I buy another car? Brakes and tires are recent, and I've really been good about maintaining any worn out parts. But I am asking for advice on when I need to "let go."