I use the same loctite sealent that is listed in the diff oil chaneg Maintenance guide, its easy tog et (even Halfords do it.
As a tip, drain as much fluid as you can out of the level plus first....then remove most of the main sump bolts with the exception of the 4 corners. Then wind the two remaining bolts which are closest to the level plug almost fully out and slowly release the other two (the sump should tip so more fluid comes out of the dain hole, you might have to encourage the gasket seal to break).
The front sump is slightly more difficult to drain but, follow the bolt removal method above to kepp it as clean as possible.
Whilst you clean the sump assemblies look for foreign objects and check the magnet for excessive swarf, make sure you put something under the gearbox as it will continue to drip oil...(a cat litter tray is very good although I use a cement mixing spot).
Its an easy job.....just smelly!