Well it looks like it's going to be a pig of a job, the alternator that was fitted 2-3 years ago is not OM but one made under the brand name Fohrenbuhl FA5181 (Andrew Page) and the cover fastenings are not as on OM, 2x screws holding the cover on, one at the front close to the rad but the one at the back out of sight
but not feel, I have just that one to get off then I can have a look at the regulator and the brushes, I have emailed Andrew page and as far as they are concerned it's a complete Alternator or nothing
searching the web has as of yet brought up nothing (unless anyone on here knows better) and i bet the parts will not interchange.