L322 Trans fail safe prog fault

Hi there I’m new to to site so thanks for having me and listening to me problems, I have a trans fail safe prog fault coming up on my dash normally after about 10 to 15 mins of the car running and when doing more than 60 mph on a bit of a hill. I took it to a 4x4 garage in Sunderland and they said it probably is the gearbox on its way out. It’s a L322, 2006 tdv6 3.0 diesel with 120,000 on the clock, it already had a recon box at 76,000 which makes me believe that it is not the gearbox, the garage took a sample of the oil and said they could not see anydebate inside only that the oil was a bit discoloured so they changed the oil and filter in the gearbox but fault is still there it comes on for a few seconds then goes and then might not come back on for the rest of that journey, can anybody out there help.
Thanks

Well its not a V6 for a start!

Anyhow - if it came up with Trans Failsafe Prog there should be a fault code logged in the transmission ECU - did your friendly garage put it on diagnostics and pull any codes?

The Td6 will eats its gearbox regularly, although 46k miles is a bit soon, it is not unheard off depending on the quality of the rebuild though! Only true 'cure' is to rebuild the box and fit the revised Sonnax valve block.

Do you have any idea if the gearbox fluid cooler was changed when the gearbox was reconned - one of the next biggest killers of the GM5 box (and the ZF5 on the V8's) is overheating of the fluid - if the cooler is blocked with crap - it won't take much to cook the fluid and then to trash the clutch plates in the box.

Thanks for the reply, forgive me if I sound like I’ve got no idea what I’m taking about but this is my first RR and I’m not a mechanic by trade just good with the basic things.

The garage did put it on the computer but he did not tell me any codes nor did I ask , he said that he was convinced that it was not the gearbox at first when he took a sample of the oil but then after he changed the oil and filter he then said it’s probably the gearbox.

I’ve no idea if the cooling fluid was replaced as the box was changed just before I bought the car , I have the receipts for the job that was done but it says nothing about that.
So does the gearbox have its own cooling system if so where is it located.