First, there should be no need to special order a heater element for your Rv system - it is a standard 1400 watt, 120v element and usually available wherever plumbing supplies are sold, including Depot, Lowes and many local hardware stores.
Where we live, there is no hardware store, just a small lumber yard and they don't carry many plumbing supplies. It's easier to order an element than drive to a city to buy one.
Second, a heater element rarely suffers a partial failure, i.e. loses some of its heat capability. It either works or burns out. If your heater works at all on electric, the element is fine.
I don't know what to tell you there. For the last week, I had noticed that the hot water in the shower wasn't lasting as long as usual, and Friday night it didn't last until the end of my shower, and that's a Navy shower. When dh went in later to take a shower, the water was only luke warm from the start and then turned to cold. That's when we switched over to propane.
Third, the water doesn't get hotter on gas than electric. It may get hot faster, but the final temperature is controlled by a thermostat, not by the type of heater. Since 2003, all Atwood water heaters use a single thermostat for gas & electric mode, so the temperature will be identical. Suburban heaters use a separate thermostat for electric and gas, but the temperature is the same for each.
There again, it may be that the element had been failing for awhile. On electric, I could hold my hands under the hot water. On propane, the hot water felt like boiling water.
The PT valve can drip a little for a variety of reasons, but the most common one is what NY Dutch described. There should not be enough leakage to have water accumulate - ithe small amount evaporates almost instantly. If you have visible water, the leak must be more than a drip.
I don't know what else to call it. It's a steady drip when the water is being heated. Not just one drip that evaporates before it hits the bottom. It's a drip that hits bottom and another separate drip on it's way down. It's not a constant stream of water, just a constant drip.