Hank, the Junior is a reliable machine. Designed to be an "international" compressor, the Junior is modular allowing common procedures like 2nd and 3rd stg valve removal to be accomplished with hand tools. The second and third stage valves are subject to corrosion after five years. They will make a clicking sound and then the second stg relief valve will blow. This is a sign that the valves are stuck. I found a way to forestall this but Bauer may not like it. After the last tank is filled, open the petcock on the interstage for 5 seconds, then close. Open the petcocks on the final filter and let the compressor run under no load. The operator will likely notice a clicking sound which is the third stage plunger banging against the push rod. I have never seen any damage caused by this but IMO, the Junior should only be allowed to run this way for 10-15 seconds, just long enough to blow water out of the third stage. If this is followed, the valves will last 15 years.
Use a quality synthetic oil of 30W viscosity (ISO 100). Bauer recommends an extremely heavy, ISO 150 oil for some of their machines but I'm skeptical that this would be suitable in the Junior. Although the oil in the sump may look clean on the stick, even after 50 hours, a complete draining will show something different. Change the oil a bit more frequently than the book says. Remember, you are in a hot place.
The Junior is a slow turning machine, faster than the Alkin but still pretty slow, with modest output and doesn't generate a lot of heat. However, as a rule, never operate the unit in direct sunshine when temps are above 85F. Too much heat hinders the filtration system and there is a slight possibility that the oil will run hot and throw off some noxious vapors.
Personally, with a rebuilt machine, I would run the unit for a few hours and then do a blowby test.