Maintain your car the way you want. OEM parts or after market. I know how you feel about the car. I have the 560SL that I bought in 1995. The 107 body came out in 1971 when I was a senior in High School. While all the kids wanted Camaros, Mustangs, Corvette etc. I wanted a 107 SL. Well I finally was able to afford it in 1990 and I finally found a cherry one in 1995. I will keep it as long as I can. New engine, sure when the time comes. Tranny etc, etc. What ever it takes to keep it. Is it worth that kind of money in 5-10 years. Maybe not but its my toy. I have a 82 300TD that I have owned since 1990. I'm putting in a new AC system, completely. Just rebuilt the entire suspension. Am I putting in more in parts then the car is worth. Probably but My wife and I love the car. In a couple of year it will probably need a paint job. and well probably do that too.
Enjoy the journey, And don't worry about just getting to the destination.

Dave

I've owned the car since 1995 and the hard top has been on it all of 2 weeks. It's a convertible, the top should be down.

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car