I have the original manifold, pre-cat and hollowed out cat. Followed by piping and RB muffler. I can't find any holes, everything seems tight, yet there is obvious fumes getting inside at normal speeds, seems to come in a bit through the heat vent.
Any obvious places it could be?

 

rear hatch seal

 

Could be a bad seal anywhere around the car. Window...door..hatch..something. Check the floorpans, maybe a leak is coming through there.

 

Hadn't thought of the hatch seal, although it LOOKS fine.
Got the new door seals, the ebay specials. Not too sure about the quality of those, however.
Thanks!

 

Its the seal for the tail lights.

 

Tail light seals are new, but that's a great suggestion. I did the 'paper test' on the rear hatch..put a piece of notebook paper between the glass and the seal. The paper slid out very easily at the bottom, not at the top. Tells me bad seal there. I put several strips of duct tape on the glass at the bottom, tried again. Paper now snug. Bet that's it..rear hatch seal.
I'll have to drive it a bit later to be sure.. thanks for the help, guys, I was looking in the wrong places (exhaust piping).