I'm pretty sure the FA and F are the same. You might consider switching to a synthetic like Redline MTL. I have replaced the Type F with MTL in two Volvos with the 4-speed + OD with very good results. The trannys shift smoother and the ODs work much better. Of course, if the OD is worn out, no oil will fix that. Do not use Dexron!

To change the oil,
1. First make sure you can remove the fill plug. Sometimes these are very hard to get out.
2. Remove the drain plug, and fill plug and let the tranny drain.
3. Clean all aroung the plate under the overdrive and remove the bolts holding it to the OD. Oil will gush out. When you drop this plate, watch for a small screen which will drop out with it. There may be a small flat magnet on the plate.
4. Clean the plate.
5. A thorough job would be to replace the filter which is up behind one of the plugs you can see when the plate is off. I didn't.
6. Replace the plate using a new gasket. Be sure not to let any dirt get into the OD or tranny. I did one with a new gasket and re-used one. Neither has leaked.
7. Replace the drain plug and refill the tranny. The M46 takes 2.4 Qt. I bought a small pump which screws on the oil container and it works great.
Good luck, let us know how it works out.