I'd like to run this problem past the experts for opinions.
The well is a 4" deep jet with metal casing extending down only about 25 feet. The jet is about 70 feet deep. The well is at a weekend home (in central Ohio) and used only for toilet flushing & hand dishwashing. 2 years ago we noticed the pump motor would not shut off. After shutting off the breaker we installed a pressure gage. The pump would build to about 45 psi in a minute or two and go no higher no matter how long the motor ran, 20 min at least until shutdown by breaker switch. We tried cleaning out the small water tube that runs to the square D switch. Nothing was found, and it had no effect. The system would hold the 45 psi (with no water usage) even for weeks. As a "workaround" we adjusted the pressure switch to operate about 40/20 psi (instead of the orginal setting of 50/30psi). It has worked OK for the last two years at the lower switch settings. The only noticable effect is that the toilet tank seems to take a little longer to fill after flushing than when switch was 50/30. The pump is a Griswold brand (Atlanta, Ga it says on it) and dates from about 1990 as do the black plastic tubes in the well. The pump sits maybe 15" off the well with a bladderless tank in 3' cement block pit. The house is at the elevation as the pump.
So my question is what (in the opinion of experienced people) is the most likely explanation? Does this sound like a partially plugged jet, silted up inlet screen, or something like a broken impeller? Also a second question, do you experience guys have any "secret tips"(like heat, big cheater bars, special oil?) for undoing rusty pipe unions? Already tried the spray oil and ample cussing but union refused to budge!