I am currently in the process of dismantling my rear triangle on my Trek Fuel to replace the air can on my RP23 shock and noticed the sealed bearings are slightly gritty. As removing them is something i’d rather avoid, would I be able to wash the bearings with white spirit and regrease? If so, what would be the best grease to use and would white spirits be the best option?

My view is that if you remove the seals to regrease them you will damage teh seals and shorten the life of the bearing. However a “gritty” bearing has already had the seal fail and is on itw way out so you might get a bit more life out of them by doing this.

I would use a degreaser or something like brake cleaner to clean them, I don’t know what effect a white spirit residue might have on bearngs.

others will tell you its possible and even right to remove the seals off sealed bearings to regrease them

Brake cleaner certainly sounds better, I have carefully taken the seal off with a Stanley blade without marking/bending it, so I’m confident I won’t be damaging it – what grease would you recommend?

Same grease as you’d use for anything else. i.e. for wheels, pedals etc etc. Just a good quality grease. I’m currently using some purple stuff.

Personally I never like to degrease (unless they are really filthy). I prefer to use lots of kitchen tissue to wipe out all the grease. With degreasers you have to make sure you get EVERY last scrap of it out before putting new grease in otherwise you have the perfect recipe for makeing the grease ineffective.
Mind you, my bearings never get that dirty because I do them regularly.

Clean with brake cleaner, repack with Silkolene RG2 grease (other waterproof greases available), refit seal and rebuild.