Jeremy,
If you didnt seal the acrylics you can most likely get them off simply using glass cleaner (Windex here in the US) the amonia in it will cut the acrylics without harming the pastic at all.

To remove the primer (provided it was enamel) both EASY OFF oven cleaner ( yellow can-like previosuly stated) or brake fluid would work with little to no affect on the plastic ( again like previosuly stated always a good idea to test on a small area first). If the primer was a lacquer based primer you will have a harder time getting that off, as just about anything strong enough to remove lacquer will most likely damage the plastic as well. You may have to simply sand the areas where the oil is bleeding through back to bare plastic.

Whichever method you choose to use, once you get back down to bare plastic, make sure you wash it well with soap and water (some people like using Blech's tire white - sold here in the states at Wal-Mart in the automotive area), then right before you re-primer use either a purpose made plastic prep, rubbing alcohol, or glass cleaner to wipe down the plastic. That will remove any dirt, dust, and/or oil and help tremendously with adhesion.

Squid