Peter,
There may be a description of this in the manual but I don't have it to hand. So what's said below may not be relevant.
There are nylon 'guides' embedded in the hull both fore and aft of the keel on the later Superseals but I don't know if this was the case for the early Baker built ones. Mine is Parker built no 103.
The nylon solid pieces are embedded in special indentations and bolted through into the fore and aft 'lips' of the keel casing. I took mine out about 20 years ago thinking they needed to be replaced (as they were wearing quite a bit) by removing the bolts ... the nuts are inside the 'lips' and difficult to get at.
Bill Parker sent me two new roughly shaped pieces of nylon ca. 20mm thick. I didn't really need to replace them.
[img=http://1drv.ms/1EtXdoG]SupersealKeelGuides[/img]
SupersealKeelguides One of the above links should get you to photos of the guides from a similar boat. If you can't access them mail me and I will send them. I can't see a way of putting the photos directly into this mail.
You should be able to see the edges of the nylon shape and the countersunk bolt heads through the antifoul ... notice that the aft one shows the keel has worn back between the bolts and is therefore also wearing through the inner fibreglass too.
Quite common I would expect and not a serious problem. Mine is worse.
Maybe there is an early Baker built owner who can confirm (or otherwise!) this.
Hope this helps.
Chris Turner (Elsa. SS #103)