Renault Espace 2.2dci 2005 crakshaft seal

Hi i recently bought a Renault Espace 2.2 Dynamique auto..this car was in a garage for 2 years without moving and encounter loads of mechanical issues most if not all have been fixed at around 2k of spenditure....its a great car in fabulous condition...the one issue i have is...the alternator belt has been thrown twice, latest one tonight since January this year...thanks to a great mechanic has been done at a fraction of Garage prices...the problem is how difficult is it to remove and replace the crankshaft seal as its leaking oil really badly...the mechanic is slightly concerned that maybe the timing kit will have to be removed and replaced...do i need a special tool to do this? Is it a major job any advice is very welcome...thanks for all your help in advance