Saving Old Seagulls

Can anyone tell me what the correct oil is for a lister sr2 marine gearbox.
Thanks.

This will depend on what gearbox is fitted to your Lister sr2.
If its a HL150, then use EP 80, or if its an LM100 use 20W50.

Thank you very much for your help Keith
20w50 it will be.
Kind regards.