Bruce,
This may be the answer.
A friend (not a TH owner) who is moored near me sent this.
I have also sent his contact details as a private email if you need them.
"There is no clutch as such. In the gearbox there are two brass cone clutches, one for forward and reverse. They are moved either side of neutral by the lever mentioned. This lever has a rectangular steel block which engages the cone clutch. This block wears and falls out of its groove (hopefully clear of all moving parts) with this block gone the throw of the lever is reduced by 2 mm either way. So the gear is never quite fully engaged. Centrifugal force does pull the clutch in but it doesn't seem to work in reverse so well.
The block is hardened steel 10mm x 12mm x 15mm with an 8mm hole from memory. I made mine which was easy enough to do, but I do have the details of the importer who can supply most parts locally or with a 6 week wait from Italy."
Phillip
SEAKA