Where is the trans axle fill on a 1990 Toyota Camry?

Look on the side of the transaxle for a plug, if this is a manual transmission. If it is an automatic, the fluid is added through the tube the dipstick is in. A manual transmission takes a heavy gear oil, usually about a 90 weight viscosity, and should only be filled until the oil begins to flow out of the hole. Check the level by inserting your finger into the hole. If it is right below the level of the hole, it does not need more oil. If this vehicle has several hundred thousand miles on it, it might be wise to drain the transaxle and fill it with new oil. If it is an automatic with more than 100,000 miles, flushing the transaxle is a good idea.