may I ask plse if u have a scanner as may give u a rough idea regarding in what fault codes appear from the gearbox
Alas seen gearbox repairs ranging from getting a new solonoid pack for the mechatronic module, wiring harness , bridge seal etc along with things like bad / low ATF oil, which seeing you’ve done repairs before indeed understand repair costs can run away with themselves
Heard this company being recommended , plus dealt with them personally and found them very knowledgeable
http://www.autogearboxes.co.uk/services.html
with gearbox replacement & TC have seen many paying in excess of 3k +