Technical leakey gearbox

[fiat 75]

had a slight problem this morning went out to my car started up ok went to move off and it felt like there was a brick under one of the wheels got out had a look nothing so tryed again and just felt like a big thump now i have the gear box oil all over my drive as you can guess the misses is not happy this is very unusual problem im a reasanoble machanic i no most things but neaver came across this befor as this is my first fiat could this be a coman problem or just a one off please help im at a loss

 

[Gary]

I have never heard of this before, thats wierd