If its the pump on the end of the cam .... then no problem .
Once you take the pump off its all self explanitory.
I didn't even disconnect the suppy hoses .
MB do a complete seal kit for about a tenner ;o)
I've never done one, but, looking at the parts drawings, it's quite a job - the flange doesn't come off the front end of the shaft, it's all one piece, which means you have to dimantle the pump to enable the shaft to be withdrawn, at which point you'll be able to fit the seal.