Seems like the FI points themselves didn't fail on my '75 450SEL, but I do remember replacing the wires that went to each set. Probably cleaned the points of pitting as well. The ignition points, on the other hand, burnt up on a daily basis, from crankcase fumes leaking past the distributor shaft seal. Wish I'd been able to figure that out on my own, but my techs kept it a week before getting back to me with the bad news-a $700 distributor back in about 1986. When a catalytic converter (I believe it was ONLY $1200 per side back then!) went while I was still mulling over the distributor shaft seal issue, so did the car. Replaced it with our first diesel 300TD wagon, with nary a problem after. Funny thing was that the 450SEL ran extremely smoothly for the one day or so that it took to foul the ignition points, and reached 20mpg on the road. Once it became clear how unnecessarily mechanical and unreliable the chain of events was to fire a cylinder, it wasn't much of a decision to dump it.
