If you are going the Merz route, shoot for something newer and turboed. I can attest that the om603s run fine on even pure gear oil in the summer. I have no experience with an om617, but I am picking one up in the spring if it's still hanging around. 1986 300SD everything including the tires and body are absolutely flawless. The owner dumped about 4 grand into it fixing little stuff only to have the tranny go down weeks later. He parked it. While one of my merz's is down due to a sudden loss of compression, I cannot blame that on the WMO fuel, becasue it was burning the exact same fuel my other vehicles ran and they are problem free. WELL, thats a lie, the compression is down on the old IDI, but it's got over 450,000 on the original engine. It also ran many thousands of pure WMO and WMO blended. It's compression slowly went down as expected even if it ran pure d2 the whole way. Two different diesel guys warned me that it would be going down soon due to the sheer amount of mileage on an original engine. Still runs, but is a pain to start and burns so much crankcase oil it's impractical to use it unless I need it. Little blue is still running strong and it has MANY many miles of pure and blended gear oil and WMO. It alone is responsible for the consumption of 400 gallons of gear oil and about 300 of WMO since I bought it. It gets a S%&t ton of miles weekly. The 94 is most likely an IDI, which makes it more attractive to me as the parts are tons cheaper for it than they are for a PSD. A reman injector is only 30 bucks for an IDI. Pump 600. You can replace the pump and injectors for what a few injectors for a PSD cost.
