heyas

I got the verdict yesterday that the thrust bearing is almost shot, need to replace over the next month or so.
At the same time, will replace the clutch ( or atleast have a crack at it myself )

My question is, i have heard the rear main seal can be replaced whilst the box is out.
Is this true, and is there much too it, or best left to a mechanic?
As far as i know, there is nothing wrong with the seal, but i'm thinking best to replace if i got access.
Oh and if it differs, it is a 4.2 petrol / gas efi gq

cheers

ozz