Stupid oil transformer connection & solution

A wise solution to have cheaper transformers was to connect the bars to the coils by rivets instead of bolts and nuts.
This stupid solution led to a lot of trouble, because in Romania before energizing a transformer we measure the resistances of the coils. If the difference exceeds 2% the transformer is considered bad.
I had many cases, one was for a waste water treatment installation from Hoghiz.
First we changed the transformer with another which was worse than first and then I fixed the problem with my friends from IRUEE Campina. We dismantled the transformer, cut the rivet and we put a bolt with a nut. We checked with the installer that it is OK and we immersed back in oil this transformer. I noticed that the rivets were slightly not at 90 degrees than the bars and the coils.
Probably this was from the riveting tool, probably held by hand, even it was hanged on a rail in the factory. The precision of the riveting is a condition of good contact.