Hey BoWeevel,
Welcome to your last preamp
1
I've used MP1 now MP2 for over 25 years now and they are still (after all these years) IMHO the best preamps ever. The thought of not having my MP2 cooking is not one I want to contemplate... They are getting older though and there are some options to give them a grease, oil and bearing change, particularly to use better more modern components and replace the bits and bobs that die over time (seems to be caps mostly ??).
Peter is the guru on MB1s, so I hope you/he can dig up his posts. MJMP is the mod master
and is sure to help...
Change tubes (always a good idea depending how old they are). I'll mostly defer to Peter here as I don't have a MB1 but JJs are usually good (lots of fully tested re-badged JJ options, Boogie STRs, Rubys, Grove Tube etc), personally I'd give the new sensor Mullard short plates a go, they are IMHO better on guitar than JJs and should have the feq response for bass, and they are sooo 3D mmmm. Then, tubes are very subjective.
To my mind, the MDRT is a no brain-er, if you can afford it, put it in (http://www.marshalljmpmodshop.net/miscellaneous_parts_and_replacement_tubes.htm), I wish there were one for my MP2.
Battery, IIRC there is a mod for that (probably similar to the MP1 battery mod), good idea (considering how old the units are)
Caps, for any that go off over time it will be worth replacing them with better (longer lasting) more modern caps
Resistors, again similar to caps, if there are better modern components ? MJMP will know..
Opp Amps, Soli (IIRC) replaced every opp amp he could in his MP1 with newer better specked (where he could) etc and said the improvement was amaizing, this is a big(ish) job though ?
Anyway, welcome to ADA heaven, cheers Richard