El Toro is right, but you do know that the rotary valve doesn't use any oil it just recirculates, so personally I would use the specified oil, and just put in maybe 1/4 tank.
You can use the TC-W3 in your weed eater, chain saw, or give it away at the marina. I had some before I got my 4-stroke Mercury and they were glad to get the TC-W3 at my marina.
If you want to save some money your 97GTI is a 717 so you can use mineral or synthetic blend API-TC oil.
Lou