RTG's are definitely a unique field and are usually designed for a very specific purpose. As far a servicability, there isn't much! Usually the only servicing performed on a RTG is the disassemby of the unit for recovery of the radioactive material, prior to final disposal. The primary isotopes used in RTG's are Sr/Y-90 and Pu-238. Both pack quite a punch due to their specific activities and ability to be shielded due to their mode of decay. Both produce a large amount of heat during their decay. The heat is converted to electric current via, (HOPE I SPELLED THIS RIGHT), Thersistors. The exchange is pretty inefficient so most RTG's are designed for low voltage operations, but for long time operations, some as long as 50+ years! Sr/Y-90 RTG's range in size from about 60,000 to 180,000+ curies and are capable of generating temperatures as high as 900 degrees "C".....SMOKING! RTG's are usually stationed in VERY remote locations and you probably wont find any within driving distance of your house, unless you happen live in an area where you could die in second due to environemental factors, (Space, middle of the ocean, north pole, ect..) There are several published incidents where individuals have found these devices and decided that their protective shields are hiding untold treasures! After busting the puppy to pieces, most never get a chance to tell their story!
RG!