Up to what year Mercedes Diesel can Amateur hope to maintain?

[Carrameow]

I have had luck and success rebuilding and maintaining my W123 83 240D and 85 300D, but I am looking ahead to see whats on the Horizon.

(1) Up to what year Mercedes Diesel can I hope to be able to service, overhaul(including engine) before chip/didgital technology makes it impossible.

(2) When the W123 Series supply runs out (ala 240D/300D) can anyone name an equally reliable Mercedes Diesel in the 87-90 model year that I can hope to claim as a Project car?

(3) My credentials http://mywebpages.comcast.net/rtc9/BENZ.html

(4) Can anyone recommend a specific car to work on and look for?

(5) I dont make much, but I dont want to have to drive a Dodge Neon or Escort. I dont mean this as disrespect, they are probably great cars, its just that my mercedes reflects me.