It is my understanding that the alu spacer is there to stabilize the rod change shaft not as a seal. When I changed mine, I left the alu spacer in place and just changed the seal. Worked fine.
This is pretty much how these work. Some of the guys on these pages have pointed out that it's not in fact after-market but they fitted these in the factory in later years. Certainly all the quite late Gearboxes I've pulled down have had them fitted.
All these Lip type Seals only have a certain take up range where the Shaft needs to be within so much of the Center, outside of which, the Lips no longer contact the Shaft enough to effectively seal, or in extreme circumstances, will lift off the shaft. The Smaller the Seal, the less allowable movement or off center is tolerable. The Aluminum Bush isn't intended as a Seal in itself, the O Ring on them isn't there to seal, but as a means of mounting of the Bush and take up for the wide tolerances of the case machining where the Interlock Spool fits.
From Timken's Seal Design Catalogue
Timken refer to the type of seal that's usually fitted here (spring inner lip, and an out wiper lip) as a 'Type 94'. According to them, the maximum this particular Seal can be Off Centre and sill work is 0.0084" (8.4 thou). While I've not actually measured it, I've found many of these Shafts have at my reconning, up to 0.020" play (or run out), well outside the range the seal will work.
In some instances, the Bush in these Kits won't cure the issue and from what I've found it can be that there's a scratch in the Bore that the seal's fitted to from a previous Seal removal, the Shaft is pitted and in some, that the Bore in the Casing is distorted well beyond what the Bush will take up, sometimes from wear and sometime from having the Roll Pin bashed in. When these are found, I've sorted them with more drastic action
by fitting a Bronze Bush in the Case.
My own experience with the Bush / Seal combination has been very good and when used within it's limits, I've found the cure the leak here every time.
