There is one PDP8/m in the museum. It has been restored to running condition. The 8m has a smaller chassis than the 8e, only allowing for a single 20 slot backplane. It also has an updated front panel using LED's instead of the incandecent lamps of the 8e. The rotary switch is also a normal one, not made up of magnetic reed switches.
This 8m is branded C/C Computer Control. It was used with an CNC machine.
With the smaller chassis and power supply, it's a lot easier to move around. Had to replace a fan in this one.
The power supply is much smaller and easier to work on. This one had a bad capacitor in the "power good" circuit which caused to generate multiple "power fail" pulses.
The bad capacitor is the long, skinny, tantalum just to the right of the large heat sink. It was all dried out.
Here's a photo of the 8m's front panel showing the LED's and the more "normal" rotary switch. I thought there was a problem with it as starting the computer running caused it to execute only one instruction, just like single stepping. This turned out to be the bad "power good" signal in the power supply. The panel was fine.

Processor boards

8k core stack