I found a Rainbow D3 for $25 and decided to experiment with the the fan and motor assembly by washing it in the dishwasher.  The armature and motor field weren't dirty, so I didn't see the need to put them in the wash.  (Sorry for the bad photo.  I had to use my phone on this one.)

My dishwasher has a "Soak and Scrub" mode on it, so that's what I'm using.  The cycle washes briefly then soaks.  The cycle takes quite awhile to complete but nasty pots come out very clean. 

The vacuum, including the motor was filthy.  That this vacuum wasn't totally fried is a real testament to how well Rainbow motors are designed. 

Something I realized when taking this vacuum apart is that the motor is actually a peripheral discharge motor.  The purpose of the plastic shroud that goes around the motor is to direct the airflow from the bottom of the motor (shown in the last picture) and up the sides of the motor housing before being vented into the fan assembly through a series of holes around the periphery of the bearing plate.  So the motor is pretty well protected from the possibility of water intrusion.  That's a change from the motor used in D and D2 models where the airflow is directed through the motor itself (like and Electrolux and other conventional canisters).  I suspect that may be why some of the D and D2 models are grounded.  I ordered new bearings.  When they come in, I'll show a few pictures of the reassembly and the finished product. 

I threw caution to the wind and ran the motor parts through the dishwasher.  I'm pleased to report that they came out just fine too.  Even the tape that holds the thermal fuses in place did well.  In the D4 motor, those are held on with zip ties.  I'm thinking about doing that on this motor, because I wonder if the wash weakened the adhesive.  But I can only find zip ties that are rated up to 185 degrees Fahrenheit.  Does anyone know how hot a Rainbow motor will get (under normal conditions)?  If they get hotter than that, I'll have to find some heat stabilized zip ties. 

I tested the motor field and each segment on the commutator with my amp meter too.  Everything tested out fine.  However, I did take some steel wool to the shaft of the armature.  I'll put a little grease on there to make sure the bearings and nuts to make sure they easily go on and off.  Now, I'm just sitting around, waiting for the bearing plate to arrive.  When it does, I'll start reassembling everything.   Sorry about the large photo.  I don't know why it's doing that!