Hello! Welcome! A plus for you is that you know the original owner and how he took care of it. Leaks are the worst situation to run into of course. Front window leaks and leaks at the front part of the roof are not all that uncommon. Lots of experienced people on here. They've been there and done it. If you haven't owned an RV before, and even if you have you should check out all of the great information available on the internet and on YouTube. You can find out just about anything by doing some Googling nowadays as you probably know.
Check this link to see if your fridge was recalled in the past.
Some folks were unaware there had been one.
Official Dometic Recall - DometicUSA
I'm sorry your dad has health problems and isn't doing well, that's hard.