Hi Rick,
Ive just had another thought after reading your last post
Since you observe that in your case a thinner washer is needed for the front stud???
The main pump body and the front portion are separate pieces, its probable/possible that these can become misaligned to some degree as its only the screws holding the pump together that keep the bits aligned????
I dislike the star washers intensly as they chew into the soft pump body
I normally fit the pump with 3 suitable allen screws with thick steel washers under the heads, I spotface the damaged alloy flat so the washers will have support
A little screw lock on the threads if you feel its neccessary,
I would put some on the screws holding the pump together
Also check for any rot in the pump body, they crumble away with age
Regards
John O R