Should I be looking for a replacement gearbox

Hi, first post on here and I've spend two days looking over the tech searches....
I've had an 01 x plate jumbo put back on the road as a bit of a toy (although it's serving as a daily driver for now too) and there are a couple of issues. When I pull away in 1st - 3rd there is a kind of groaning bearing whining noise. There is loads of vibration when pulling in all gears but I do have a polybushed transfer box. I dropped the gearbox oil yesterday and fully expected a load of debris on the plug but had barely a covering of super fine dark sludge ( the oil was clean and no burnt smell). The rear gearbox mount however is delaminates and I can lift the box with ease so I've ordered a genuine one and it's due tomorrow.
When I look up at the rear mount the centre bolt is about 10mm off centre! When I fit the new mount, should I loosen the front engine mounts to re-centre the rear mount properly? I really just wanna get it right so I don't end up with bigger bills lol
It's the M13a DOHC if that helps

Many thanks for reading and I look forward to any and all advice/banter..... Gav

Fitting the rear mount will fix your issue. In fitting the mount you will align the engine and gearbox; there is no need to touch any other mounts.

But should the middle bolt be dead centre? If so and when I replace the mount the bolt is off centre, how do I get it to centre? I'd think man handling it into position would simply put the new mount under stress and make it fail quickly?

A video on fitting your mount:

It is currently off-centre because the mount failed, not the other way around. It moves easily- this will all make sense when you lift the gearbox up to fit the new mount. There is no adjustment or alignment to worry about.

Well I'll say a little prayer that it's the magical fix to some bloody awful noises lol

No magic about it. Your gearbox is currently unsecured, floating about hitting metal on metal against the remains of the mount. With the new mount it will be secure again.

Well the mount arrived and I've just removed the old one which had totally separated and looks to have been for some time!! Upon fitting the replacement, as I feared the centre bolt to the box was not visible and too considerable lateral force to get the bolt hole there to attach it. Now I know that there is something amiss as that lateral force will constantly be pulling on the new bush until it fails :/ would loosening and then tightening the front mounts allow everything to even the loads on the bushes?
On a super positive note.... Jimbo has lost all of that God awful noise in 1st to 3rd and pretty much all of the vibration too!
Thanks for the advice as I'm still learning

I'll check and report back

Just a quick question....
When I look into the engine bay should the black plastic cover on the rocker cover be flat from side to side? Mine tilts to the passenger side by a few degrees. I think the engine mounts feel a little "soft" when I rock the motor so I'm gonna buy a pair too.

Hello there. I have the same issue with the noise in 3rd 4th and 5th gear in. I got the noise after changing the clutch I think the mechanic forced the gearbox off or on the engine and a bearing is on the way out. You can align the gearbox with the rear engine mount by playing with the front engine mounts just loose the bolts and stick a big screwdriver and use it as a lever to move the engine left or right there is few millimetres free room on each side. I got the rear engine mount dead on the centre however it only slightly reduced the noise also changing gears got little smoother. I am not changing the gearbox unless it gets very bad I have done over 20 000 miles and no issue only the noise still there