There is - and all of it contradictory! Less salt, more salt, drink less, drink gallons ... I've asked my doctor, and got nothing definite there either, other than "it's your age".
I used to have very little salt in my diet, and started adding a bit to things like porridge (mmm, yes) and peanut butter. It improves the flavour, but hasn't made any difference to the cramp. Trouble is, it's like an intermittent fault on a car - it doesn't happen reliably, so you can't attack it with logic and a diagnostic approach.
That would be nice - perhaps I can copy this message to my wife. She decided she wanted a walk-in shower a couple of years ago, and we took the bath out. The only time I get a hot bath now is when we go away. However, although I am sure this would help, it doesn't uncover the cause. I can't see anything I am doing on a 6-9 month cycle that might make it happen. But a proper bath would be brilliant, if someone could speak to Father Christmas
Anyway, I don't want to take the thread over, so I'll shut up.