200tdi injector pump leak. Easy gasket?

Hi
Diesel was pouring from my engine today.
Had a look and it was peeing out from a bolt on the side (right hand side, nearest the wing) of the injector pump. Noticed the bolt was loose so tightened it, slowed but didn't stop the leak. Its clear where its coming from, out of a seal behind a lemon shaped plate on the side, see photos.
New gasket? I've got a gasket set somewhere. Whats behind the plate? If I take it off is something going too fall out? I normally try and leave injector things alone, I normally make things worse.
Thanks

http://i1382.photobucket.com/albums/ah258/billiam122000/DSC_0107_zps4g7esyqe.jpg
http://i1382.photobucket.com/albums/ah258/billiam122000/DSC_0109_zpsj4ti9ngt.jpg

Nowt will fall out, well...didn't on mine when I removed that plate.
There is a rubber seal underneath that's failed.

I think thats the advance mechanism, wammers is good on inj pumps.