In reply to PPP:
I've had no problem with petzl torches - Myo RXP is my go to for climbing / mountaineering and the Tikka RXP for running / general camp and bothy use. Neither have had any corrosion problems despite repeated soakings and some quite hard use! Petzl are more transparent about their lighting standards / times as well so win points from me for that!
If you are looking at other brands - some Fenix torches are fully waterproof (friends who sea kayak use them for that purpose and a local MRT to me uses them as well - though the models that they have are no longer made and the replacements are not nearly as good!).
Alpkit I'm slightly wary of - cheap and cheerful, but I've had 2 fail on me, and friends have had similar. Great service from Alpkit - instant replacement, no argument from them, but it's the risk you take with a cheaply made torch. In fairness another mate has had a gamma for 3-4 years now with no issues at all. Mine is now the car / DIY torch.
LED lensers are good and feel very robust as well as putting out a good quality light - probably worth a look. Though it's only the H7 and H14 that I've tried.
Magic shine do cheap head torches, but be wary of their ratings - very much the bad practice end of advertising (i.e. the ratings are max output from the LEDs rather than the actual light in the setup advertised, and represent the peak output with fresh batteries, with run time being until the torch dies rather than any the ANSI standard that many use or petzl's own lighting guarantee).
Sounds a bit like you need to take better care of your kit if your finding that it keeps wearing / breaking across all the brands you try too though.
Good practice to remove batteries from your torch if it's going to sit for a long time not being used - helps avoid corrosion problems in the battery compartment (same as removing them from an avalanche transceiver when it goes away at the end of the season). Also definitely get the torch out and dried off (inc battery compartment) if it's got wet! Like everything, the better you look after it, the longer it'll last.
Cheers!
Stu