First, I have enormous respect for the B747 - a great aircraft to fly on.
It must be admitted however that the early days were quite tough for maintenance. The three leased Pan American -100 we operated ate Pratt's -3B engines at a rate that reminded me of the old Wright 3350 on the Connies and DC-7. There was little relief there until in later years (at another carrier) we celebrated the removal of the last -3B model and replaced it with the greatly improved -7.
Then there were the turbine reversers originally fitted. Until they were finally deactivated it was a constant thing to be shoving the sleeve back forward and locking them out. The early engines had little stall margin and thunderous booms were pretty frequent.
I can never forget the multiplex passenger entertainment system. It consumed a whole crew of radiomen to maintain. Occasionally a zone units would overheat and start dripping smoking resin from a transformer. The smell was unpopular with the pax.
When converted to freighters many aggravations went away. I found them to be much easier to maintain with all the pax gear stripped out. Strangely, I never had anything to do with any later models. Wish I had.