Help!!

Have just put down a depost on a 57 plate Vectra. Looks pretty clean all round, but a couple of niggles and one slightly weird one which I need help on:

Under the bonnet I was having look around (I dont really know what I'm looking for) but noticed that one of the suspenssion mountings was rusted on one side but not the other. Asked the dealer and they didn't know either, so I'm now paranoid as to whether this is a walk away moment or actually its nothing serious?

What you see is the plastic cap on the top, a ring / cover / cap of rusting below and then the painted bodywork. The other side has no rusting and its just the galvanised finish. Have had a look around web sites and cant see if this rusted section is structural / mechanical or just a cosmetic cover - can anyone help??? WHat I have seen on the web is replacement top mountings and they dont look like the rusting piece I saw under the bonnet. Its just strange it rusted on one side and not the other.

Any advise gratefully received as I dont know if this is a big issue, costly item, or just paranoid me.

Gordon