If it's an RV fridge, are you sure is has a compressor ? Does it also operate on propane if you switch it when you're camping ?
Alot of those use a hydrogen charged system and plugging them in merely energizes a calrod heater to cause a reaction in the gas. Oddly enough, these systems can become "stagnant" and require only to be removed, shaken and turned upside down overnight to reactivate the combined gasses.
For most of us, it is illegal to keep filling a knowingly leaking sealed system - filling it for testing purposes may or may not be. I normally use high pressure dry nitrogen with bubble solution to locate such a leak.
Monitoring the high side pressure will be kinda useless and will add to the leak by providing another likely path. Usually low side pressure is monitered during testing purposes along with visual frost pattern - using a pierce valve is NEVER recommended, and the mapp gas will not heat quick enogh for the easy flow or silver solder that is required.
Bottom line is that there is a good chance there is a leak in the evaporator (seems common with those) and the compressor may now have damage from operating full of atmoshphere. Since this is the second such repair that may indicate a leak in some of the unexposed inner cabinet tubing - repairs of such issues are iffy at best even for well seasoned and equipped specialists.
Comes a time when you need to cut loose from these - cabinet modification to fit a different unit is much simpler/cheaper/more reliable.
This is an indication that the element has been overheating due to an inadequate exhaust vent. I have never seen a roof vent that worked properly (moisture laden air will always "fall") you likely need to replace that element, clean the whole dryer out and reroute the vent so it exits straight out the house as short as possible with as few elbows as possible.
I like the Kids' Bubble Blowing toy's (the bottle of solution with applicator built into lid) - available in the Kids section at WalMart, much cheaper and it works great as long as you keep it from freezing.
Then again, when I'm around - there is usually little doubt that there is indeed a gas leak as you never get past the odorant