E Class Questions
I had to reply to your post because I had the same questions about a year ago. I have always owned RWD Volvo's (still have two) and do all the repairs myself. I found a '88 Mercedes 260e in mint condition about a year ago that I couldn't pass up. I bought it because it had a SOHC straight 6 that looked pretty easy to work on.
The MB E Class cars are very similar to a Volvo in handling and comfort. I think the Mercedes has the same solid feel and control of a Volvo but definitely is a lot quieter. MB put a lot of design effort into soundproofing this model and it works. The engine on my car runs extremely smooth and has good power for a 2.6 litre. Mercedes engines rev much higher and that took me some getting used to. Another oddity is that some 4 speed auto models, like mine, start in 2nd gear.
As far a durability, I still feel that nothing beats the Volvo 4 cylinder. As you probably know, those engines almost always outlive the cars. The MB engine has the same durable bottom end but needs periodic head work. Some common items needed are: valve stem seals, valve guides, and head gaskets. I have not done much work on my Mercedes look but in studying it, it doesn't look too bad. The tools needed are different...lots of hex stuff and the working room is tighter. Parts are comparable in price to Volvo. I have used Fastlane and was really impressed with the prices and had the parts in a couple days.
To answer your question about the straight 6 and V6, I think the change was around 1994 or 1995. You can tell by the badge on the cars. The 260 and 300 are straight 6's and the 320 will be a V6 (I think). I'm sure someone here would know for sure.