150 optimax fuel pump problems

I’m having problems with my Optimax 150 fuel pumps, both the low pressure and high pressure pumps. After sitting for a couple weeks they seem to “seize-up”. I’m able to get them running again by removing the pumps and reversing the polarity. I run carb-cleaner through them thinking they are gummed-up. I need to reverse the polarity a bunch of times (probably 15-20) before (specifically the low pressure) will run continuously-more than 5 minutes. Each time I reverse the polarity it runs a little longer. Starting at about 15 seconds and increasing by 5 or 10 seconds each time. The low pressure pump will not run continuously in reverse polarity but eventually runs fine with the correct polarity. Does this make any sense?

Both pumps have been replaced, the low pressure was replaced twice. I’ve looked at the gas and so has the marina with no problems. I’ve drained my gas tank twice but it doesn’t seem to have solved the problem. All fuel lines have been replaced. I have (2) filters on the fuel lines, a 10 micron particle and the under the cowl fuel/water separator. Should I replace the 10 micron with a Racor? Although I haven’t seen water I’m wondering if this would help? I have a 72 gallon tank that’s 21 years old that I could replace (but it’s expensive) without knowing this is the problem.

I’m open to all recommendations and suggestions. I can’t keep replacing fuel pumps at $300 each!