The best way is to strip her down. many people have been successful with the 3 bath dunk method. soaking in naptha over night. That does get most of the crud out and does work. people have reported they get another 3 or 4 years of reliable service after that (we once had many DIY sites).

But the problem isnt really that the wash doesn't get everything.. its the relube that is the main problem after such a wash. Bottom pintels of gears arent easily accessible so they get lubed. Grease in critical areas that are buried under other parts are ignored. Even in the ultrasonic bath, that does a better job cleaning but like I pointed out, its the relube that will be lacking.

If you arent going to strip it, send it out for a professional cleaning. If you have nothing to lose... DIY by dunking or ultrasonic.

Whatever you chose to do, get the manual so you at least have an idea what and where to lube and with the right oils n grease. You can find tons of information on teh web if you spend the time to research it.