Hmmmm, I had the same thing happen to me over December. I took the kids on a 3 day fishing trip to the Vaal Dam, with trailer hooked up. The Iron Maiden cruised perfectly there and felt no difference in power. However when I got home, there was a squeak coming from what I thought was the belts, so having not changed them for a few years, I bought new belts, and proceeded to swap them out only to notice that the Alternator shaft was very wobbly. Turns out the rear bearing collapsed and disintegrated into quite a few pieces !!
You probably have the original Hitachi Alternator. These are difficult alternators to work on, due the regulator being inside the casing, where as the Bosch style alternators have the regulator accessible from the outside. There are 2 routes you can take. The original Hitachi is probably a 60amp which is fine for our non electronic TD42's, but due to me having a duel battery and a whole load of extras like 2 x 130 watt spotlights, fairly powerful sound system etc etc, I wanted something that kicks out a little more amps than the 60 watt original and to be easy to repair if in the middle of nowhere. I carry a spare regulator with me ( cheap and lighter than carrying a spare alternator ).
You can get higher amp Hitachi alternators from companies like Probe ( http://probegroup.co.za/
) or you can get a Bosch alternator or even something like Chuck or Arries fitted ( Delco ). As long as its the ( J180 - I think its referenced like that ).
Your Hitachi can be serviced but apparently from what I hear the guys don't like to work on these cause its a bliksem to get to the regulator inside the unit.
It all comes down to what you want out of the alternator..... remember you can never have too much power....