Congrats on your purchase.
1 - You can fill the oil through the yellow cap.
2 - I replaced my 6v batteries almost 3 years ago with 4 from Costco, they were $89 a piece.
3 - As for the jack, they are Power Gear, and electric. I would replace the bent leg. If it is jammed up in the housing, you will shear the pin in the top of it before you will get it to lower.
Since it is a front one, you can easily repair it yourself once you have the part. The fronts jacks are easily accessed by extending the slide out.
All you need to remove the jack is a 3/4" wrench and a 3/4" ratchet.
Remove the 6 bolts holding the jack to the frame bracket.
Take the jack, and remove the 2 bolts with nuts on the side of the leg. You should now be able to drop the piece that extends out of the motor assembly.
Remove the bent leg, and install the replacement. Make sure the magnet on the leg extension is facing the sensor on the leg. This tells the jack when it is extended, and when it is retraced.
Reassembly is reverse of assembly.
I would also check and verify the jack motors have been weatherized. If they have been done, there will be a metal clamp holding the boot to the motor.
If there is a plastic wire tie holding the boot on, you will need to remove the boot and check the brake for corrosion, and if none, put the boot back on, and secure it with a metal 3 1/4" hose clamp, and silicon the top of the boot, as well as any wire entrances, and the area where the motor is assembled.
If you find the brake is corroded, you have 2 choices. Try to clean the brake up yourself, or replace it.
I cleaned mine, and they are still working to this day. I do carry a spare just in case, they are $89 from Fleetwood.