+ about 100

OK a few things may have happened. Steel into aluminum can gall the threads even if they are OK. Prolly paint and dirt in the old threads ... a thread slightly "off" on the new fastener.

I am constantly amazed at how bad the threads are on stuff coming from China. I've had to repair and throw away plumbing fixtures, SS bolts, and one new tap in the last year becasue they were all out of spec, out of round, or wrong pitch ...

In any case, it's prolly in there tight. So it'll be a bugger no matter what ...