I purchased a 1990 300E early this summer for $7,000. It has 150K miles on it. It began missing badly in July and I took it to my mechanic (whom I trust). The problem was a bent valve and a head that needed machining. I took care of that. The rough idle is back and my mechanic has found oil fouling my plugs. He suggests I think about a total engine rebuild, since the oil rings are likely bad and given the mileage, etc. The vehicle is in otherwise tremendous shape and rides beautifully. It also has a newly machined head. I have three questions:

1. Does a rebuild seem the right thing to do or are there other alternatives?
2. What am I likely to have to pay for such a rebuild?
3. Given the mileage on the car, what other repairs (non-engine related) should I expect? Transmission? Suspension?

Thanks!