Question for Metallica owners, is there any difference in the build quality between first run LE's and current runs of Metallica? I have played both and found the current one feels lighter and is much easier to nudge.

I know this could be due to set up, but other current Stern pins seem the same, current Lucy ACDC wobbles on it's legs and Iron Maiden feels cheap and light like an IKEA toy.

That's because heavier usually does mean better quality, the lighter pinballs on wobbly legs IMO are not as good to play as the more solid older pins that don't fly across the room with the slightest nudge. Stern has been lowering quality all around for quite a while, this is just another example.
I wanted to get more info so that I know how to pick an older more solid one if I decide to buy a Metallica.
TBH I like the playfields of IM and JP2 but IM feels cheap to play, everything just feels flimsy and the QC issues are shocking so sadly I'm another who won't be buying NIB, that's why I'm considering Metallica.