Hi Edgar

To check the o-ring, all you have to do is unscrew the front half of the starter housing. Before moving the starter motor itself, mark a line on the motor at the edge of the threading. This will ensure that you can reset the motor to the same depth afterwards. Remove the starer and check the condition of the o-ring. If it is badly worn, simply reverse it and re-install it in the starter bendix.

If this doesn't solve it, PM a phone number and time I can call and talk to you.

Sincerely,
Ed