When you replace the starter just use any normal grease on the large 'O' ring. Put the 'o' ring on the starter before you place it on the crankcase and when you put it on check to see that it is firm before doing up the screws. Don't use thread sealer on the 'o' rong.
See how you go.
Bruce
Regards,
Bruce
Please do not PM me asking for support. Post on the forums as it helps all members not just the individual.