transmission failsafe

Hi folks , I'm one of a long line of L322 lovers ( were all nuts , I know I know ). I've currently got a very nice 4.4 V8 which has developed a issue with the box. It drives fine when cold , but when it heats up it selects fourth ( with a thud ) when driving and emits "transmission Fail safe " on the dash. A little investigation on this leads me towards a clutch "O" ring seal within the box that apparently goes after a few years and requires replacing .
Just wondering if anyone has had a similar issue and what the issue/fix or fixes were if possible please. Thanks for reading and hopefully replying.

Scott

I've got a feeling that this problem can also be due to the transmission oil overheating. I have a diesel but I'm pretty sure the petrol box (although different) also has a small oil cooler for the gearbox which gets blocked and puts the box into failsafe mode when the oil gets too hot.

Or it eats itself

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