Geneseeing is believing! Not rotten eggs, somewhat different than that. Pretty sure the spider is to blame. More along the gaseous noxious fume line.. but only at brief intervals (coming to a stop at a light after some spirited driving).
There's numerous threads on dealing with gas smell, but oil could be quite a few things from leaks spraying the exhaust to a mis-connected or gumed up oil vapor seperator, or even the diff or trans spritzing a little bit of hot gear oil here and there. (cooked/cooking gear oil is pretty rank compared to motor oil BTW)
ok, cork sniffing complete... After much deliberations with myself I'd say we are on the gassy fuel-smell with a whiff of super-heated catalyst gasses. Essentially when I come to a stop the cloud "catches-up" with me and then dissipates. Also despite having the head rebuilt earlier this spring, I get a small bit of blackish-grey smoke if I really stomp on it from a dead stop as run through 1st and 2nd, and is no longer apparent in 3rd.