I was surprised to see no responses to your post. Its possible they were lost during the two recent database problems on the board. Ill give my response, and if it repeats what youve already heard, I apologize.
Most manufacturers have a service system set up through their authorized dealers. If you got your equipment through your local dive shop, check with them. At my LDS, the various manufacturers whose equipment we sell come by from time to time to give repair seminars. After completing one of them, you get a certificate that might then let you repair that equipment. I say might because there are sometimes more restrictions. For example, my LDS only lets DiveMasters and higher attend those seminars. Then you have to get the repair manuals and service kits again usually through an authorized rep. And besides standard hand tools you usually need some special gauges and tools (many available from the same place that sells the Wolfinger book, below), and usually a sonic cleaner.
At least one place,
Hall's teaches equipment maintenance.
Some books that can help you understand regulators:
Vance
Harlow's and Pete
Wolfinger's
The first includes hints on how to work outside the system. The second gives a more thorough theoretical grounding.
Im told that DiveRite now sells their service kits to the general public.
Thats the short story about regulators. For cylinders, it would be a good idea to take the
PSI course.
And then there are cylinder valves, compressors, boats and their diesel engines, swimming pools, etc. etc.
Hope this helps.