Suggestions for cleaning exterior of 4spd

Oven cleaner is good, but crystal Draino is better. It is the same stuff that the machine shop uses to hot tank ferrous metal. You will need to remove any aluminum because it will react with it. It is sodium hydroxide......lye. It is nasty stuff, so if you use it, be careful. Wear eye protection and gloves. You also do not want to inhale the fumes, and keep your face AWAY when you are handling it. Even the dust can cause you problems if you accidentally inhale it. You simply mix it with water to the strength you want. Oven cleaner has the same basic active ingredient, but nowhere near as concentrated, and the drain cleaner is way cheaper. Cheaper still is powdered lye from a feed and seed store for instance. But, you will probably have to buy a larger quantity from there than what you need to clean the transmission. You'd have more left over for future projects. Just mix it up and brush it on with a paint brush and let it sit. You may need to do it a few times. Course, you could disassemble it and soak the case, but it does not sound like you wanna go all that far. I remember when I worked in a machine shop when I was younger. The boss hired a new guy and he put a set of pistons and rods in the hot tank overnight. The pistons were about 3/4 gone the next morning. Lye does NOT like aluminum. Mixing it with the hottest water you can also ativates it even more. But again, I warn you, it is dangerous stuff. If you get any on you, stop what you are doing and wash it off NOW. I have used it for years with great results. It works better if you have an immersion tank, but if you keep painting it on a few times, it will do the same job. Since it is water based, it rinses right off with water and becomes inert once it is diluted enough.