I've also got the black-hardware adjustable, and with the hard water in Orange County I need to clean it every 3 months or so or soon enough I can't open it at all.
I use an electrician's contact cleaner--CRC QD, I think--that's rated safe for use on plastics. It works very well for me; it's got plenty of petroleum distillates in it, so it's not something I'd use right before a shave, but the bad stuff is well and evaporated by the time I'm done cleaning.
If you've got hard water as well, dilute muriatic acid, CLR, or similar might be worth a shot. I haven't tried vinegar either, that stuff works well on my stainless appliances for water scale. I stick with the contact cleaner because I know it works, it won't damage my razor (muriatic should still be fine for the plastic, but I don't know what metals Gillette used and wouldn't be surprised if acids started etching that over time) and it's something I always have on hand anyway.
Nano-oil or CLP break-free might also be good choices, but I rinse my razor thoroughly so I'm not sure they'd actually last that long before the water scale starts building up all the same.
Maybe mineral oil (food grade) or some sort of grease after cleaning would help. Hmmm...