Padlocks often difficult to open

No, it's mineral oils so it will cause natural rubber and SBR to swell (rather than rot). Nitrile is immune.

My thoughts too. That link gives six of them for $20!

Worked fine for me every time.

Costs peanuts and that squeeze bottle lasts forever and WD40 costs more anyway because you have to keep using it.

Mine tend to be filled with grease. Not for lubrication but a protection against *politely advised* trespassers coming back with some superglue!

Jim what exactly is the action on a fan belt that makes it last longer ? i once saw a mechanic give one squirt of wd40 on a fan belt to stop it squeaking.

bollox

Most DIYers usually have a can of WD40 secreted somewhere about their person, so it surely makes sense to use it (even if you do have to give 'something that needs doing' a very occasional quick top-up squirt)?

The propellant has probably changed since the '80s, but a misdirected squirt of WD40 crazed spoke-mounted* reflectors - possibly polycarbonate(?) - actually, could have been polystyrene, as that would be easy to damage with a freon.

I once tried to 'wash' a nailbrush (which I had been using for cleaning something greasy) in white spirit. The handle (polycarbonate, I'm sure) immediately crazed, then it all disintegrated into loads of small pieces before my eyes.

However, I can't recall WD40 doing any obvious harm to anything I've used it on.

Never seen anything that dramatic, but "environmental stress cracking" is a well known issue for many polymers.

If the problem is rust in the mechanism then graphite power is unlikely to make any difference. The OP indicated allotment use and a padlock design possibly not suited to even keeping a minium of water out of the mechanism. The brass case and shackle may be rust free but what about the inner wheels and spring?

I bet these cheap Yales contain steel

See above