Z-track.
I do subcutaneous injections and get tiny oil leaks sometimes too. It used to freak me out. To gain perspective I tried placing a square of clean toilet paper to absorb the leak. Then, I took the syringe I used and drew up some tap water, same quantity as my T dose, and emptied it onto a separate square of tissue to compare.
The leak was tiny in comparison to what the full dose would look like, obviously not worth freaking out over. Additionally I get leaks less often with a slight modification in technique. After injecting I keep the needle in for at least 15 seconds, still applying pressure to the plunger. Have a square of tissue handy, quickly withdraw the needle, and place the tissue over the site to check.
Bottom line is that your T levels be stable within target range. If that's the case then clearly a dribble of oil now and then isn't screwing things up.