I have had a few merc’s of this era, not one of these though, I would look out for rust, rust and suspension issues, otherwise if it works properly it will probably carry on working for a long time! I had a c class 2.0 petrol that was still going strong at 250k but too rusty to bother fixing.
You can buy brand new generic remote servo kits on ebay for a wide range of older cars, you just need to know if your pipes are metric or imperial. They are priced from about £90 upwards. I intend to fit one on my mk2 Tina when I get to putting it all back together.