Right guys as promised, this was the final outcome of replacing the bearing, first off, I have to apologise about saying there is no mention in the workshop manual about a master spline, I got that totally wrong there is even a photo showing it
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With the shaft off the car applying WD40 did no good, in the end I had to lay the shaft on the floor and hit some of the bolt hole lugs using a copper hammer and it did eventually come apart.
I have to say with it still attached to the car no amount of levering would have budged it.
Even after getting it apart and locating the master splines it had to be hammered back together as it certainly wasn’t a sliding fit, even after greasing it.
I used a bearing puller to remove the old bearing from the shaft.
On fitting it back under the car I found I’d knocked it together slightly more than it should have been and as a result the bolts wasn’t quite long enough to go through the flanges and rubber flexi joints allowing enough thread to get a nut on, so I used some all-thread to get it started.
Once the shaft was extended enough I swoped the all thread for the original bolts.
The only thing I could not replace was the rubber gaiter which covers the splined section of the shaft, it appears its longer sold by Vauxhall and I could not find anything near the size, so for better or worse I’ve used some sealer to try and make good the old gaiter, I’ll keep my eye on it from time to time.