I don't really want to argue too much about the boiling thing because I don't really care what other people do. But for the sake of information, I'll finish off my thoughts about it with this:
- In the real world, it worked excellently for one guy (me). It may or may not have worked well for others, but I've never seen first hand what others are doing, so I cannot vouch for their success. It's possible that I am (and other people who have written about this are) spreading bad advice. Your mileage may vary. Your experience with this (or lack of experience with this) may be different than mine.
- You're taking safety into your own hands if you decide you want to rebuild, modify, or work on (in any capacity) a safety critical system. Please, do not do anything you're not perfectly comfortable with. If you read something on the internet that does not seem logical or comfortable to you, just don't do it.
- As mentioned before, rebuilding MCs may not make much sense. Other's have pointed out: fully built MCs are not much more expensive than a rebuild kit. I'm doing this because I'd like to learn something new, I don't want to throw away something that can be repaired, and I'm dumb.
From a factual perspective:
- DOT 3, DOT 4, and DOT 5.1 are all soluble in water (polyethylene glycol base). Rate of dissolution and total solubility both increase with temperature, but agitation only increases the rate of dissolution (not the total solubility). For similar amounts of build-up, ultrasonic cleaning may have similar results when using water, but may require longer exposure to the water and require more frequent changes of water as the solution will reach saturation more quickly.
- Corrosion of the steel parts may increase in an aqueous environment, especially if it's in contact with an electrolytic solution (e.g. salt water). Rate of corrosion increases with temperature, but I'm not sure how it changes with agitation (my guess it is there's no appreciable increase). I would not recommend reusing any of the steel parts (but you bought a rebuild kit, right? Then who cares what happens to the steel parts as long as they come out.)
- The aluminum body may be damaged by both basic and acidic solutions, so careful selection of your cleaning solution is important. Distilled water will not damage aluminum at boiling temperatures during this amount of time, but tap water may have some residual minerals, salts, or metals, or have an imbalanced PH. This may cause the aluminum to corrode. The alkalinity of some common/popular cleaners (such as Simple Green) will damage uncoated aluminum, and may damage coated aluminum depending on the type and condition of the coating. Be careful what solutions you use to clean your aluminum.
- There may be some galvanic corrosion of the aluminum due to conductive contact between the steel parts and the uncoated aluminum bore of the MC body. This corrosion will be minimized or eliminated with the use of distilled water due to the lack of an electrolytic solution closing the circuit between the anode and the cathode.
