Hey dude, welcome to the site.
The A4LD front seal issue can be a little more complicated than just a failed seal.
They can fail when the converter bushing in the bell housing wears.
The transmission can also puke all it's fluid out through the front seal when the engine is allowed to get low on coolant, runs hot which runs the transmission hot... barfs all over the ground. You can usually top up the coolant (fix the coolant loss issue), top up the tranny fluid and you are good to go.
If it is the bell housing bushing, they have to be turned to size while in the bell housing. PITA.
If you are just changing the seal because you have the tranny out, treat it like any other seal, make sure you stalk it in though.
I am sure you have already been in the tranny section, lots and lots of good info there. Have a look at Glacier's A4 rebuild thread, probably explains how he installed the seal.
Rock on.
