[Alan Wheeler]

OK, thanks for the update in technology then. It sounds intersting. Lets hope it will be economic price wise and economic output wise.
Int he past, Stirling engines mostly used two forms of heat. Steam or direct flame to heat air. Thus the ability to lubricate was not higly efficient. The result was that the engine had to have work "maintenance" carried out on it from as low as 500hrs for some to a few thousand hrs for others. The difficulty was not so much that it had to be serviced, but the fact that units were often hermeticaly sealed and service by just anyone was not possible. So the engine had to be returned to the manufacturer. It was not bearings that were the issue, it was the piston/cylinder wall that was the problem.
If these new coolers have found away to lubricate those two contact surfaces, then I guess there is no reason a unit could not run for as many hrs as any other fridge compressor.