“Clutch” Failure

[Mike523152]

My 75 2.0 CDTI is currently in the garage with a “clutch” problem, basically changing gear became increasingly difficult over the space of about 1 week and very few miles, no noticeable issues previously detected with the clutch and the AA mechanic thought it was a hydraulic issue. Car was towed to a mechanic and they tell me they can’t identify the cause of the problem until the gearbox is removed and only then will they be able to tell what is up with it, DMF, clutch, master or slave cylinder etc. is this correct as the cost to remove the gearbox alone isn’t cheap.
I have AA breakdown and parts cover which will cover a part if not all the costs providing it isn’t due to wear and tear and or clutch failure. I am concerned that I am going to get stung by the mechanic and or the AA on this, can anyone offer any advice on what if anything I should look out for to prevent being screwed over with this.