Did mine not so long back. Haynes book of lies tells you to drop the gear box, but after some advice on here I pulled the engine. Spent an afternoon getting ready, draining coolant, removeing all the crap necessary, then did engine out, new seal fitted, new clutch fitted and back in all in 1 day. Refitted all extra bits following morning and running again. Had help from a good friend during strip out and replacement which made life easier.
I would recommend buying a genuine LR seal, cost about £18 as I would hate to find a pattern part was NFG. Seemed logical to have a clutch to fit too, while engine was out. As it happened the old clutch was on its last legs and needed doing anyway. With engine out, its also a lot easier to do cambelt, so you may want to consider doing that at the same time if its due before too much longer