I put together the components for electrolytic rust removal and tried it out on some unimportant pieces of steel. Worked very well so I dissembled the level and wired it up.

Old battery charger, container and water with a bit of washing soda. Steel wire used to attach level and another piece of steel. The negative to the level and positive to the sacrificial piece.

After about 40 min. and a light rub down with 0000 steel wool. Turned it a couple of times in relation to the sacrificial piece.

The bottom - compare to the photo at the top of this thread.

Very small pits at the end - rust was heavier here.
The charger was putting out about 10 V and 0.4 amp. I used well under a tablespoon of washing soda for about 3 quarts of water. Baking soda works as well from other info on the net.
The top of the level has black stippled paint - this was not effected by the solution but a couple of very small areas near the edge lifted due to rust working it's way underneath. They were touched up with gloss black paint.
The method works well as it is not destructive and easy to do. The water solution should not be toxic - I put it on some weeds so will watch to see if anything bad (or good) happens.
The only problem I see is that a dark staining remains on the metal - will experiment as time permits to see if this can be remedied (perhaps rubbing with vinegar).
John.