1991 190e - Purchase advice?

[lartrak]

I found a 1991 190E 2.6L for sale. It looks like I'll probably be buying it. A lot of people here are super knowledgeable, much more so than the people I've been able to find at shops and what not, so I'm asking here...

I'm aware of the wiring harness issue that many Mercedes have. I've heard varying things on the range of cars and years that are affected. Most say 1991-1996, but I've heard a few claim 1992-1996. Obviously, this makes a difference. Is there anyway to check the harness and see if it is already degraded, or will degrade, at a glance? Of course, I'm going to have a PPI done, but it'd still be nice to know how I could check myself.
Also, if someone can tell me a rough price on having it replaced...I've heard anywhere from $800 to $3000.

Also, I was a bit curious about how the transmission should be shifting. The transmission sounds and feels very smooth gear wise, but when switching from (I believe) 2nd to 3rd the speed boost is larger than I would expect based on getting into the highest gears on the interstate, where it is almost unnoticeable. Typical? It may be I am simply unused to the transmission, which is clearly of higher quality than the ones in the Ford's I'm used to driving.

One final note: is paying an extra $110 ($270 VS $160) for the best PPI worth it? The car is in great shape in every way I could tell, so I dunno. I don't know how good the more expensive PPI is at a Mercedes dealer, which is where I'm taking it.

I hope I'm not being too presumptuous by making this my first post. Any advice or information is very appreciated. Thanks a lot!