First, welcome to BGW!
I just got a G1 a few months ago and a short time later the linkage end fell off the butterfly valve. It definitely will make it short on power. I'd try wiring it open to see how the performance changes. If you have access to a compression tester that will give you some additional information.
I'll be curious on what the responses are to which oil everyone prefers as I've wondered that too.
Check the square tubing frame above the rear mud flaps (usually left side, but mine was on right) for stamped serial numbers. It should also be on the engine housing near the flywheel. There is a sticky for serial number lookup and you can find out the year of your cart.
Keep asking the questions and you'll receive much help. This is a great group!