A lot, depending upon what needs to be done. Two years ago I had my mechanic dig into mine as my oil leaks were becoming unmanageable due to leaking head gaskets. The big issue that we had was that many, many parts had to be replaced due to age - plastic parts, rubber parts, etc. etc. and this all adds up pretty quickly in $$. Also, you find things that you want to get done "while you are in there" - timing chain, fuel injectors, etc. My experience tells me that you will be in to the $5-6000 dollar range if you only need upper engine work done, and you really won't know that until you get the heads off. You might be better off buying a replacement engine, depending upon how long you want to keep it. I am sure others can give you more info. Good luck!

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John Gillespie
1988 560sec - 192k miles
2006 CLK500 - 40K miles
1995 E300 - 202k miles