Well looks like I need a at least one new new drive shaft as mine are too corroded and the new reluctor ring on the left won't go on at all, the right one is siezed on and a special tool is being sent from their sister garage later on to see what's that is like.
Ahh the joys of owning an old M car....
Car is out of action for 2 more days at the min depending on when the new drive shaft(s) get delivered to the garage quick or not. Best option just replace both anyway as they'll come with the rings attached already and it's only time before the opposite side rusts itself away and damages the new ring anyway.