Is this a case of 'great minds think alike' or 'fools seldom differ'? Sorry Tony, couldn't resist. I like to think the former.. But it is a question I have often thought about. I could, like you, spend time googling but thought there may be some expert on here who would say 'Ah, yes, good question. The answer is '.
And I admit it was brought back to mind by reflecting on an experience a couple of years ago with an LGU (.177) which was making about 11.2 on receipt but over maybe 3 months of intermittent use lost maybe 2 ft lb. A new spring sorted it. But I have heard of others who found the same with LGU springs ... weakening over time.
Cheers, Phil