Hi Nino
nice work as usual.  You are right about Stern using crappy quality metal.  Target banks in particular have severe wear when there is metal to metal contact.

They are not your usual Stern flipper base plates - they look like a cross between the 1st generation and the 2nd generation (which they should be).  The gen 2 normally sit off the playfield, and the flipper stroke is limited by a separate bracket rather than the end bent up like the one you have (see https://www.pinballlife.com/classic-stern-flipper-base-sub-assembly-left-or-right-staked.html) .  Wonder if it is factory?
cheersIan