Thank you, Mystic Pools LLC. That is encouraging.

As it happens, after some grinder and die work I was able to salvage enough threads (3/8-16) to, I think, keep the assembly from figuratively jumping up and down or wandering about. When I install I think I'll try lightly snugging the new nuts down just a tad past finger tight.

FWIW, replacing the pump led to discovery of several "errors" by the last "plumber" (pool business employee who installed my pool heater) that requires that I perform a significant revision of the plumbing configuration. This was found to be best achieved by tying down the pump in a slightly different position with new studs (SS this time) so it is the one fixed coordinate in the system. A loose pump moves around too much to easily align everything, in my view.

And a word to the wise: Leaving the filter housing (Hayward DE-360S) drain plug off between seasons will advance the residential prospects of some courageous mouse, with attendant damage to the filter elements.

We have two pumps (cleaner & waterfall). Neither is bolted to the pad and don't go Anyware when running. Only would jump around if the impeller became unbalanced for some reason. Ref rodent: I had to remove the side panels on our heater to deter nesting pack rats. Also installed some solar LED lights since they are night creatures.

Good to know. My reason for bolting became one of stabilizing the pump around which other assemblies had to be connected, mostly with rigid PVC. The close fit of the filter diverter assembly right over the pump was the most limiting parameter of all. Youall have convinced me that once all is in place, I could remove the nuts without fear of failure. Hayward does specify bolting down, perhaps for legal reasons.

My Speck pond pump is also bolted down, but this has merit mostly in speeding alignment when re-installing each spring.

Did your pack rats bring you anything of value?

Our pump have to a filter basket which is connected with a short piece of 3 " (I think ) of pvc to a valve from the pool. Here is a pic

Pack rats here use pieces of cholla to protect their nests so not very nice. They and mice like to visit cars to chew on wiring (which is soy based these days) or build a nest if the car isn't used very often. A lot of people w/o garages open the hood when they park over night. My version is taking off side panel so it is not a dark place during the day. Second line of defense are the lights.

Without revising the entirety of my pool shed plumbing, my filter is next to the pump, but the filter outlet and inlet ports are aimed at the pump side from about a foot away, and they connect to a large diverter valve (filter, bypass, backwash, wash, discharge) which was originally laid-out to be over the pump. So the distance from the pump discharge port on the pump top to the diverter inlet port on the diverter side is about 10 inches at best, within which there needs to be a disconnect means and near perfect radial alignment at the ends. I'd supply a photo but at this moment there is a massive rain dump on-going that my tools just missed enjoying.

Have you considered hiring feral cats?

No pussy cats but do have bobcats and mt lions. Hard to train though. Also have coyotes and diamondback and other snakes but same problem. Wish it was raining here so the temp would drop down from 110. Good luck on you endeavors.