Yard Man 18hp lawn tractor gear oil

[zpa]

I've been thinking of changing the gearbox oil for quite some time now. The tractor is from '87 and I guess the oil has never been changed. Gearbox is a fully manual unit (as in non-hydro). Few questions I've been pondering:
1. Correct oil type
2. Best oil to avoid leaks in the future with old seals (absolutely none atm)

If I was to change the oil now, I'd probably use 75w-90 dino. Any suggestions? I don't have any manuals for it.

 

[Fleetmon]

Most of the manual transaxles I've seen are grease, not oil. I realize this doesn't answer your question though. JD, Scotts, MTD use grease that I've experienced.

 

[zpa]

It does have drain and fill plugs on it, wouldn't that suggest oil?

 

[zpa]

After some googling, it seems that the transaxle is a Peerless 2300 series unit and it does indeed take gear oil. 2 qt is apparently the correct amount.
Internals look beefy, nice

http://www.weekendfreedommachines.com/discus/messages/17/231920.jpg