Just happens I have been doing exactly the same thing with the pump out of my '72 350SL.
Problem is that we can check the rotor part out, but not the internal part where the fuel flows through the motor.
I took the check valve off, filled the motor with carb cleaner and shook it. Did this a few times dumping the contents. Saw some stuff come out, but not much. I have heard of people running the pump backwards, but that would require a fitting in place of the check valve that would allow reverse flow.
My pump was working, but I thought it might be contributing to a hot start problem. The gas flows right by the internals of the motor, so if the windings are hot, they could cause the gas to vaporize, especially when tank level is low.
For anyone dismantling their pump, make notes or take pictures of the orientation of the parts. That little notch in the plate must be pointing the right way!
There are some aftermarket or rebuilt pumps (Airtex, Python, Walbro etc), but my guess is that they are not the same quality as the original Bosch. But, list on our pump is about $850 and best on-line price is about $450.
It seems to me that we should be able to use a pump meant for a K-jet car. The exit threaded fitting for the K-jet hard piped banjo fitting would have to be removed and replaced with an elbow that the check valve off the old pump will screw into.
I would like to find the technical spec for the D-Jet and K-jet pumps before I buy a pump. The test minimum flow for D-jets is 2L/min (30psi) and for K-jet 1.5 L/min. But the K-jet is pumping against a much higher pressure.
Her's a few pics of my pump project!
Overall arrangement - helps with re-assembly!
Check valve at discharge
3 pics of pump dis-assembly
Fuel damper (part 182 in drawing)
My pump was loose in bracket and hoses needed replacing, so at least I got that done!