I checked SM 246 and it had an AUTOPROP with open bearings, so, you probably have the same kind. Unlike the later models, which have sealed bearings with steel balls, your prop has stainless steel balls on open tracks. Although they don't really need it,
you may grease these balls from the outside. This will prevent too much scaling on the balls.
If you feel the bearings make a grinding noise, then it's time to replace the balls and tracks, which you can order from Brunton's. The stainless steel balls don't stand wear as much as the steel ones (which rust, nobody's perfect, that's why they are
sealed with grease nipples for renewing the grease).
No grease nipples on the first model of the Autoprop.
FYI (everybody) hull #259 has an Autoprop with sealed bearings, the change is around 250.