Thanks for your input. Couldn't get through to anyone at Sanger and turns out it is a Walter.
I took a look around this evening while I was changing out a fuel filter and found that there is actually a plate on the front port side of the v-drive unit, which specifies the model number, recommended oil and change interval, which is pretty handy.
Anyway the low down is that I have a Walter RV26, it takes SAE 30 and should be changed after the first 100 hours and then every 500 hours thereafter.
The plate says that all Walter units with model RV10 through RV50 take SAE 30 oil.
I also found a Nautique manual online (
http://www.planetnautique.com/CorrectCraftManuals/2005Air.pdf)that had very detailed information and illustrations on changing the v-drive oil (they use the exact same Walter units); turns out there is a drain plug in the back, two magnetic plugs diagonally opposite (front and back) and a strainer to clean out.
Anyway, hopefully this will help someone else looking to do the same as it'll only cost a couple bucks for the oil (only takes maybe a quart I believe, but I'll compare it to how much comes out when I likely do this tomorrow) as the level is currently right at full.