Passat (B5) :: 2000 V6 Hard To Start - CE And Emissions Workshop Lights

I own a 2000 V6 Passat with 68K miles. For the last 3 months, I have had check engine & emissions workshop lights. During the last month, the car will not start at random times (although never first thing in the morning, only after it has been recently driven); this will happen 1 or 2 times a day. After waiting 1-2 minutes, the car will usually start on the 2nd try; it has always started by the 3rd try. Once started, the car runs fine, although there is initially a strong gas smell. I took the car to a local mechanic, who changed the air mass meter, which had no effect. The mechanic now wants to change the O2 sensors. Unfortunately, I do not know the codes. By the way, the car had an emissions workshop light in 12/04: the light went off when the dealer did work under a "WE recall", which I believe means that it replaced the secondary air vacuum line.