Does the wiring harness need replacement more than once on the W124?

[G-Benz]

Car ran beautifully after the head gasket and reconditioned top-end nearly two years ago.

Car started developing a slight miss, then eventually turned into a low-rpm bogging.

It has gotten considerably worse, to where it even backfires, and now almost always misses, bogs down, and such, as if there is a short in the harness.

Going to take the car to my indie this weekend, but I thought I'd ask...I had the main wiring harness replaced several years ago with the improved version (back in 1999 or 2000).

Is it possible that even the replacement harness has gone bad with the same insulation-deteriorating issues?

So far, the fuel filter had been changed when my indie did my last oil change service a few months ago. Nothing else. He didn't have time to diagnose the problem back then, and it didn't happen often enough for him to get a feel for the problem. But I'm trying to get an idea of what I may be dealing with, $$$-wise.

Any thoughts?