Everyone makes mistakes trying to learn how to fix their vehicles. And as most here have posted, some mistakes cost big bucks!
I have made several blunders, but the dumbest (and most recent) was the gauge cluster pull on my R129.
About $6 worth of bulbs had burnt out, and since i had already pulled the cluster out of the W124 to do the same, I figured I get them both out and make one trip to the store for bulbs.
Got a bit too impatient with the pullers and CRACK! There goes the gauge cluster lens!
Of course, SL parts usually run for a king's ransom and this was no exception...$372 just for the lens!!!
So I walked out of the dealership with $6 worth of bulbs and an almost $400 hole in my credit card!
Needless to say, I NOW work on the R129 with the same caution as someone defusing a live bomb!:p