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UTD offers a service tech course for their regs, Part 1 is online only and has video material for servicing, manuals etc etc. Part 2 is IF you need a Service Tech certification and is done in person with an instructor, stripping and servicing regs.regs made by Aquatec as mentioned above. Unsealed pistons so make sure you rinse them REALLY well while they're still wet if diving in the salty stuff and be careful in the cold stuff, same as you would any other piston.
No issues with them though but on the self-service, you're likely on your own as far as a service manual