Changed the o-ring and the bottom seal under the bearing in the dizzy today. No more leaking oil all over the exhaust!
Got the gear off carefully with a hammer and a vice. Put it all back together and although I don't have a timing light it's running ok. It needs a bit of tweaking but it idles very smooth at 1100rpm.

Heres the part numbers from CBC bearings if anyones interested -
plain encased seal - High temp Viton red - TC12379VI
O-ring - BS217

Theres another oil leak somewhere near the crossmember, probably from the oil temp/pressure plug, should be an easy fix as well.