The filler cap on the 1200's is on the right side, ( foot brake side ) right near the dip stick.
My owners manual for my 1984 Honda GoldWing says to use SAE 10W-40 Oil.
That is where you add the oil.
No
I use SAE 10-40 takes about 3.2 liters. You have a dip stick also.
Yes, it is. However, there is separate gear oil in the final drive of the Goldwing, as it is shaft driven.
same as the engine oil
No reverse was not available till 1988 GL1500
100x90x15
Yes you can use a Full Synthetic Oil in your GoldWing. I recommend Amsoil 10W-40 Advanced Synthetic Motorcycle Oil (MCF) Hope This Helps
3.9 quarts.
look for a oil cap that you take off on the valve cover.
The oil fill is on the right side of the bike (as i f you were sitting on the bike), just to the rear of the right rear cylinder. You may have a chrome cover so you may need to remove it.