AN UPDATE...
Took the RR to a company called Re-engineered transmissions in Essex and they have taken the GB apart and have just called me with some news.
The damage found is the following: one drum due to overheating and apparently the bell and oil pump housing are very worn out. He said that he had sent the parts away to try and get them re-shimmed and hopefully get my box fixed. The total cost for the reconditioned torque converter, re-shimming, friction plates and everything else that they call soft components, if it can be reshimmed is £1050.
If they can't re-shim the bell and oil pump housing, then he recommends to just get one of his recon boxes, which come up at £1350 including the reconditioned TC. And this is even before checking the valve body, as it has some damage, it will cost between £150 and £300 according to his quote.
What are your thoughts on this guys please? Does it sound right?