Welcome and you found the best place to ask question about your Georgetown.
I use the cheapest ATF at Walmart.
ATF with DexronIII and Mercon 5 if you plan to replace and flush the system.
I think its never good to mix different ATF fluids and I'm sure the factory or past owner used the basic ATF because of the costs.
The level in the tank should be about 1/2" to 3/4" from the top of the tank when everything is up and closed. If you over fill you will get leakage out the filler cap and that's messy.
You may be able to get new stencils from Forest River.
You can call them and ask but I suspect it will be expensive.
Here is some contacts.
Forest River Warranty Georgetown
Forest River Parts Dept. 574-262-2212
Dan Evans – Parts Department
Contact Phone: 574-206-7605 or 7600
Contact Email: email@example.com