Last evening I did an inspection, in which both of the original bus bars on the main service panel were used as neutral bus bars, and apparently not bonded to the panel, nor connected to the separate grounding bus bar, which was added to the panel, attached to the side (which had no enamel) with nuts and bolts.
The house also had mostly non-grounded wiring (1953 house), with many grounded-type (3-prong) outlets, which, of course, are incorrect if not GFCI.
The grounding rod (copper) and water pipe grounding (aluminum) connections were connected to the grounding bus bar, and the neutral connection from the service entrance cable was connected to the neutral bus bar. The grounding wires were also double-tapped at the bus bar (copper and aluminum).
There was also an aluminum jumper across the water meter, with galvanized pipe downstream of the meter, and copper piping into the meter. I could not confirm the compatibility if the clamps, but the ones across the water meter had contact screws that looked pretty rusty.
This all seems wrong to me, but I wanted to bounce it off you to see if any of it is acceptable, and reasons. I can see why this system with isolated neutrals would function under normal circumstances, but it seems to me the bonding would be very important in case of a lightning strike or major short circuit, especially given the non-grounded wiring present in the house.