The part that you more than likely need is the oil seal, P/N 641533. The housing is removed via three nuts and washers. The gasket you need is P/N 641538. It is probably likely that the generator/alternator will have to be removed to replace the tach housing gasket. There are two gaskets for this installation, the one piece gasket P/N 36100 that seals both the gen/alt and the tach housing or just the 641538 that seals the tach housing. It would be hopefull that you have separate gaskets... If you have to remove the gen/alt I would recommend draining the engine oil or you will be looking at a very large mess... Ask me how I know