Funny, I haven't noticed any finicky problems with my car at all....no stalling, (undiagnosed) hesitation problems or what not....The KE-III system is actually very easy to maintain and diagnose, all you need is a multimeter that reads duty cycle, temperature, ohms and voltage, and the factory service manual..... As compared to the wiring harness issue with the M104 that could result in all number of problems that are very hard to diagnose. Of course the fix for this doesn't seem difficult, just expensive for the part....Personally, as a DIYer I think that the M103 is a better motor to maintain and work on...Not that I'd snub my nose at the M104 and hesitate to work on it either.

Another issue for me is that the 2.8 M104 was only made for what? One production year? My personal preference is for the tried and true...and for which finding parts for is never a problem. The Mercedes E-Class Owner's Bible lists the 91 and 92 motors to be the most 'sorted out', with issues like oil consumption addressed by switching to Viton valve seals, and changing the material of the valve guides to prevent excessive wear. Both M103 and 104 motors can suffer from leaky timing chain covers, and both can develope a head gasket leak where the motor blows oil into the coolant. (Mine did, fixed now)

It sounds like the sender for the oil pressure gauge is broken, or the wire to the sender is disconnected or shorted...I would insist on fixing that first, ($65 part) and have the car inspected by a local mechanic. Can the 91 owner produce maintenance records?

Bottom line for me is that you can go and inspect the 91 and confirm its condition. With the 93 on eBay, caveat emptor. It could be a perfectly good car, but how can you tell for sure?

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On the plains of hesitation bleach the bones of countless millions who at the dawn of victory, sat down to wait, and waiting -- died