Disc based version here, oily textures appeared on second or third or fourth install (honestly, can't remember now) then went away after a period of extended play (8+ hours) then came back on reload. Saying that, after doing another reinstall as per the Xbox Support fix, (and updating the game) again, they've vanished. I'm on a 250GB Slim 360, and I've started a new game, too. So, maybe delete whatever save files you have.
Some folk have suggested messing around with TV settings, switching from HDMI to VGA, and changing resolution to 720p with varying results.
There doesn't seem to be any correlation between console, or disc versus DDL and issues - freezing, bad pop-in, bad textures etc (although a majority of complaints seem to be from people with older 360s and the disc version, possibly due to the media coverage it garnered), and R* haven't acknowledged any of these issues yet.
Definitely send a ticket to R* support, as the more reports they get, the more likely we'll get a response/patch.
EDIT: Also, to note: I've installed the second disc, as I've mentioned before, and the only difference is slightly improved FPS and slightly worse pop-in.