Your initial post says that the RPM goes up? We may be on to something here. MB's of that vintage were affected, believe it or not, by surface rust on the teeth of the ring gear. This condition resulted in flywheel acceleration being affected during starter engagement. The CKP interprets this as a running engine and aborts the crank. I've seen this many, many times. The tell-tale sign is a brief chirp when the starter gear meshes with the ring gear. Listen closely and let us know what you hear.