There are actually 2 of these rubber 'grommets' one above the other. The top one that you can see is more of a dust seal really [in fact there is a drain slot between the two].
It is the lower of these grommets that is actually responsible for sealing the oil inside the motor.
While you MAY be able to make an effective repair with silicon from the outside you will probably need to remove the advance pulser cover on the back of the motor {is fiddly due to confined space but can be done without removing the motor]
This will give you access to the lower grommet which can then be lifted out, cleaned up and resealed with silicon. Also smear some silicon on the individual wires and slide them back and forth through the grommet to seal the wires themselves.
Be gentle with the wires, after around 30 years in a hot oil environment the insulation has hardened and become fairly brittle.
Clean up any excess silicon as you don't want this stuff floating around in the motor.
You will also need to fit a new gasket to the cover, either buy or make one.
