In the old days we used ATF oil, or air-tool oil. Anything but WD40.
If the orings are swelled, or if its full of dried paint, you might have small issues. But otherwise not much to fail.
Your tank can't be worse that the rental tanks you usually see. Fortunetly, smaller 7oz tanks are practically given away. Granted, given the effeciency of the VM, you are going to be filling that sucker after every game. Its pretty trivial to add a bottomline for a bigger tank.
__________________ www.montneel.com "the evidence strongly suggests that neither Billy nor Adam (Smart Parts) could have invented the electronic paintgun" -Garr M. King, U.S. Judge