This page is posted primarily for historical purposes, and so you know what you may be buying these days. The original style rear seal for the early 1500 gearbox may be no longer available. In the pictures below the seal on the left is original type, and the seal on the right is the current replacement type.

From the outside they have similar appearance, a steel cup with a felt dust seal. The primary difference is the new part has a rubber lip seal where the original part has a leather lip seal. The new part also has a completely cylindrical outside diameter, where the original seal has s step in the O.D. being slightly smaller diameter for two thirds of the length.

The view inside is substantially different. The new part is basically a steel cup with a piece of felt and a modern garter spring shaft seal pressed inside, very simple. The original seal has the felt part plus a leather shaft seal. There is also a somewhat flexible expander piece plus another steel cup pressed in to hold it all together. The leather seal puts much more seal material into contact with the shaft, and it may be more tolerant to the sliding motion of the propshaft coupling.

This is admittedly a design surviving literally from the age of the steam engine, or earlier, but all things old are not necessarily bad. I have seen these leather seals in service for the original life of the gearbox, some running intermittently for 30 to 40 years, and still functional. I have also seen many a rubber seal die of old age in a decade or less, sometimes just a few years, commonly suffering from embrittlement and cracking, especially when exposed to heat.

Unfortunately it is difficult for me to recommend exclusive use of the original style seal, because they are likely to be unavailable. This is one of those cases where we make do with what we can get, and if it's cheap enough and it works well enough to get by for a while, then we may never again see the original type part.

Addendum December 2011:
The original type early rear seal with leather and felt is now available new from Anglo Parts, their part number 023.011, picture below. This appears to me to be an exact reproduction of the original design as in pictures above left.