Larry has some good advise, if you have the later sending unit. I had exactly the same problem. 1st suggestion would be to get a new cork gasket before you remove the sending unit unless it has been replaced recently. After you remove the sending unit, you will find a nut on the bottom of the canister. Carefully remove that nut, and cap. I used aluminum duct tape to cover the very small holes on the side of the canister, that allowed me to fill the whole unit up with rubbing alcohol. (Thanks to JA 17 for that tip) I let mine sit overnight, and then very gently used a small cheap paint brush to wipe the float guide and the very fragile wires inside the unit.
The above info is not for the earlier sending unit found on the 230's, and the early 250's. This only applies to the later canister sending unit. Let us know how it goes.
OPPS I now see that you do have a 230. Maybe some other members can help with a solution to that problem, as you do not have the late canister sending unit.