hi there,
I removed the front calipers on my previous red rover , split them, and glad that I did.
The oil transfer holes from one side to the other were completely blocked and needed a lot of poking and prodding to unblock.
The kit I bought from England included the small rubber o ring that seals the two half's completely.
That is what you need, I guess that it is special rubber and not just old " O" ring material, because of the oil.
I followed the workshop manual in reassembly and nothing leaked and the brakes again worked as they should.
Don't be afraid to split the two half's, its how they were assembled in the first place when manufactured, scare tactics to ensure that they can sell more new ones ?
Alas that car is now in another owners hands................sigh
Peter