Rocker Cover Gasket, did they know that was under the bonnet... bl**dy hell.
Noise in rear end, unless something is broken it sounds like a worn bush, tie-rod or similar, which 'should' be easy to find. Shame the shop couldn't find it, but I doubt you need to go back there.
It isn't difficult with a pair of eyes and not much else.
As for suspension shops in Melb, sorry no idea... great shop in Geelong though.
Pole Position, do some lovely work with Koni's, Bilstein, King Springs and Whiteline stuff...
Anyway, I have a R33 GTS-T with Koni's, lowered king springs, whiteline adjustable swaybars and Strut braces front and rear. Fairly firm and 'tuff' ride but sticks like glue...
Coilovers would over a little more setup variations but will be probably firmer, like RS73 said.
Would love to go for a ride in BLISTC's setup as it looks and sounds good, especially with adjustability, but pretty sure that Coilovers will not fix the noise. They will also not generally offer you the same standard of comfort based ride that a V35 is famed for.