What is the proper lubricant for the loading bolt on an Airsoft sniper rifle gun?

I have a relativly new airsoft sniper rifle (VSR-1O Mauri Clone from buyairsoft.ca). I got it roughly3 months ago and havnt lubricated it since then, so the bolt for loading it is getting kinda hard to pull, and i think it would be bad for the gun not to lubericate it. If anyone knows thatd be great!