At some point en route back from LMC2012 the tail seal on my Sport gearbox started to leak and deposit oil on the underside of the car. Is this a common problem and what is involved in the replacement?

Cant comment on how common but from the boxes I have tackled with this issue, it isnt a difficult job normally. Only worry is if the seal has worn a groove in the shaft.

Its a reasonable DIY.

Thanks. Only 16k miles and leak only started a week ago.

That should help to keep any rust under control...
Speaks the former owner of old Brit bikes (and half a dozen Land Rovers)