Since I bought my Champion used back in the 70s I didn't have any intructions about any probs with getting the inside of the blade thing wet. I dropped the original cutter housing and broke the little tab in the back that kept it locked in place and kept the housing from spining. When I looked into replacing that I found that for a little more money I could replace everything but the motor ($60 total) so I went ahead and did that., The core of the older cutter is metal so I can see why maybe they adviced against getting that wet. The new cutters have plastic cores. They prolly advice against getting it wet cause the motor shaft is not stainless steel and it will rust with a wet core.
I have been washing them both on the dishwasher with no apparent adverse effects I'll lube the metal motor shaft occasionally with a little coconut oil. I don't use the heat drying cycle on the dish washer. Both because it consumes a lot of power and because it can damage anything plastic in the washer. I just pop the door open an let things air dry.