some bumpers can be a total @rse to remove, most vag genuine ones are ok, but i wanted to remove the big bumpers on my old blue mk2 years ago and got the socket on them, they turned and loosened a bit then the nut which is actually on the bumper irons spun (as it is either pressed on spot welded to the irons) i couldnt see how they hell to get em off as there was no access points to the nuts ... same on the fron and the rear... so i tightened back up as best i could and left em......
ive heard people have similar probs with small bumpers too when trying to upgrade to big bumpers.. things rusted solid etc.....
cant think what bit your on about whats been welded on yours??
Gaz