Keith,
To get at the felt seal, you will need to remove the sprocket/shock absorber assembly. Then undo the 6 1/4"BSF nuts around the final drive assembly. The whole final drive can then be removed from the 'box (you may need to use a large drift against the RH end of the shaft to start it moving). With the assembly removed, you will see the bearing is retained by a large nut and tabwasher - with these removed, the shaft can be pressed out of the bearing, revealing the felt seal. The shaft also has a short sleeve pressed onto it that fits the bore of the felt seal - this may also need replacing. Always make sure you oil the new felt well before assembly - a dry felt can quickly cut into the steel sleeve.
Regards,
Eddie.