Shim Change and Mileage

[Dead Eye]

There needn't be a caliper fault, though an overhaul is a good idea anyway. A bent disc can be caused by incompetent drivers giving the bike a nudge when parking… if they get the angle right they can easily apply enough force to bend the right disc without knocking the bike over if it's on the sidestand.
Whatever, it certainly sounds like you need a replacement. I get about 40k from them and have bought second-hand ones on ebay several times without a problem, though splashed out on some new EBC discs about 18 months ago.
If your bike is still on the originals then the bolts will be a bit stiff. I prop the wheel up over a low flame on the stove for twenty minutes until the alloy is getting uncomfortable to touch, then they can be undone without any drama because the heat weakens the thread lock and expands the screw holes due to the different coefficients of expansion of steel and aluminium.

Pretty sure this was supposed to go in to the Front Brake Discs thread that FizzyPies started...