If your Rolleiflex images all look like mid grey tones, it may be due to a hazy lens. The haze may not be visible just looking through the lens at the shutter blades, unless it's really bad. One way to check for haze is to set the lens to full aperture, open the camera back, hold the shutter open, and look through the lens at a small source of strong light, like a bare light bulb. If there is much visible haze, it will be enough to kill contrast. You will probably need to disassemble the lens to clean off all the haze, as most of it is probably on the surfaces between the groups.

This has been my experience with some old 6x9 folders I bought. The lenses looked fine until I sighted through them at a light bulb. The haze was really bad. I didn't shoot any film with them until after I cleaned the lenses, so I don't know how bad they would have been, but these were uncoated lenses, a triplet and a Skopar, and contrast didn't look bad at all after I cleaned the lenses. If you search some of the photo sharing sites, you can find images made with old folders that have very low contrast. Some users like this. I'm pretty sure the lenses were about as hazy as the ones I got before I cleaned them, and I had to take them apart.