I have a 50 gallon electric water heater in my house. After a pressure spike (100 psi) from my municipal water company my T&P valve began leaking. I added a pressure reduction valve and got the pressure to 70 psi. The valve continued to leak so I replaced it. The new one leaked so I reduced the temperature of the water from 140 degrees (which it’s been for 5 years) to 130 degrees, it leaked again. At this point I can only assume that the bladder in the expansion tank (6 years old) was damaged by the pressure spike. The existing expansion tank is 2 gallons, should I get the same size or bump it up to a 4 gallon? Thanks in advance for your help!