trying to locate exhaust/gas smell

Hi all,
Last month I purchased 1996 SVX LSi (96,000 miles). A few days after bringing it home, it became obvious there's a leak somewhere and I'm having trouble pinpointing it. It's been to 2 Subaru dealerships & they can't find anything either. Ideas would be appreciated.

The problem is a strong smell of either gas/exhaust fumes (I can't identify which). Most prominant upon acceleration, and with the heater running.

The car has had most of the exhaust system replaced, the water pump & timing belt done (along with a few other things). Nothing appears to be leaking, but the fumes are a doozey.

It goes back to the Subaru dealer I bought it from in a few days to have one of the O2 sensors replaced (but I don't think that's the cause of the smell). Any ideas for where to start looking would be appreciated.

Sincerely,
Brenda G.