Black(ish) smoke, oil leak or..? Options

[Corvius]

'94 gt, 100k miles. When I bought the car the guy told me he had the seals in the engine replaced, and the car never blew smoke. Now, ever since I made a SRI, reset air/fuel ratio, and (maybe this doesnt matter, it was a while ago) used lucas fuel injector cleaner, the car blows out a nice cloud of blackish, blueish smoke when I start it. Is this oil leaking? It only does it when it has been sitting for a while (ie. if I drive to the store, turn it off, and come back out 10 min later and turn it back on, no smoke). I gotta go to my mechanic soon anyhows for clutch work so I'll have him check it out, but was wondering if this maybe isn't a problem or ..something else..
--Thanks guys

[edo17982]

It is a known issue of FE heads especially.
It is due a very small amount of oil (very very small don't worry) passing through the valve guides to the combustion chamber.
I've read about it somewhere but I didn't save the link..., anyway it is not cause of bad valve guides, it's just a pretty common issue so as for now it's not a problem
Anyway keep an eye for any oil consumption in excess to verify that