My shower diverter is activated by pulling up the stem located in the faucet spout. The existinb diverter has been in service for 30 years without any service. My problem is that from full strong shower head output, all of a sudden the output reduced at leaset 50 %, a spray that hardly will rinse soap out my hair. This happened before and I believe when the weather warmed up, the full amount of pressure returned. All was fine through the summer here in Clovis CA, but now in December, the pressure reduced at least 50 % all of a sudden, again. I removed the shower head and tested the flow which seemed to be a steady flow but hard to tell if it was flowing full pressure. I even replaced the shower head with a full flow shower head. Nothing impoved. The maintenance man came and when he turned on the shower, the pressure improved to about 65% of what was. What could be causeing the "SUDDEN" changes and what can be done?