Back when I learned to dive there was a BSAC 3rd class lesson about regulators. Our club's equipment officer brought a couple along, took them to pieces, showed us how they worked, put them together again and adjusted them to breathe nicely. Those of us who were mechanically inclined then had a go for ourselves.
If you asked at the local dive shop they would order a service manual for you. Some regulators even came with a basic manual in the box. You could buy any spare part over the counter.
Nowadays, any such lesson would be superficial at best. Service manuals and parts are restricted to authorised dealers and only manufacturer trained service technicians are allowed to fit them.
When I am paying for a service, it's nice to know the technician has been trained to do it properly. Indeed the manufacturer and dealer both have a duty under HSE rules to ensure that anyone who works on the equipment in a commercial situation is competent and properly equipped to complete the work.
If I want to buy spare parts I get blocked at all stages:
"HSE regulations prohibit us from selling you spare parts."
"But I am not doing it commercially."
"It is possible you could be doing it commercially."
"But then it would be me who is breaking the rules, not you."
"You don't have the correct training."
"I'll pay for the training course." Most manufacturers' courses take a couple of days and cover the entire range, not just a single model.
"We are not in the business of selling training. Training courses are restricted to our dealers."
"Suppose I take a third party training course?" There are commercial organisations that do very thorough training courses covering all aspects of servicing and repair.
"We don't recognise any courses but our own."
Lets take a step back from the specifics of diving equipment and take a wider view of things. None of the rules manufacturers are hiding behind are specific to the diving industry. They apply equally to cars, lawn mowers, power tools, boats, electrical appliances, central heating… I can't list them all. The rules apply equally to all work environments, but not outside them.
I can go to the local DIY shop and buy all the potentially lethal electrical bits and pieces necessary to re-wire my house. If I made a mistake I could easily electrocute myself, electrocute someone else, or even set fire to the entire street. Yet the shop does not refuse to sell me parts on the grounds that only the manufacturers officially trained technician is allowed to fit them.
A car is potentially lethal. It has thousands of moving parts and failure or incorrect fitting of a fair number of them could cause a serious accident. Yet no one even questions my right to buy parts and do my own servicing should I choose to do so.
I could go to the local car spares shop and buy all necessary parts. I could go to the local main dealer and buy a service manual and all the thousands of parts to make a car from scratch. It has a counter dedicated to part sales. The only control is that after it is 3 years old it needs an annual MoT.
Scuba regulators have very few parts. Some manufacturers have even been known to boast in their advertising how few moving parts there are in their regulators. Yet the sale of spare parts is restricted. It sounds to me like an abuse of the manufacturers position.
Some divers will be highly distressed by the direction of my argument. Maybe they are not mechanically minded. Maybe they have been indoctrinated by the commercial training regimes to always pay for manufacturer approved servicing.
Most professional scuba technicians take great care and pride in their work, but we all have stories about divers who have just had their regulators serviced. Like the diver who turned his bottle on and saw bits of second stage shot across the boat because it hadn't been screwed up properly. Or the regulator that was a bit of a drag to breathe because the second stage diaphragm was back to front. Or the regulator that breathed wet because the diaphragm was missing completely. Or the first stage that flew apart because a circlip had not been seated correctly.
If someone is sufficiently interested in doing their own servicing, they will be motivated to take the time and have the patience to make a good job of it.
Professional servicing is usually excellent, but it is by no means a guarantee of quality, and DIY servicing is not the route to instant death some manufacturers would like us to believe. Is diving equipment really a special case? Surely we should be free to choose.
There will be people out there complaining about my "irresponsible" attitude to a critical piece of equipment. Rather than wait I will answer them all now. First: adequate testing before use. Second: I could create analogies for many situations outside of diving where the DIY approach is perfectly acceptable. Third: I always dive with a fully redundant air supply, though I have never had to use it.
Not all manufacturers and dealers are choosing to interpret the rules to maximise their service trade. Some will retail parts in quantities of one or two at a time. Enough to do one's own servicing and enough to enable emergency repairs on an expedition. That's a free market.