The grease we recommend is the Dow 111 silicone grease that is normally used with vacuum pump tubing line connections.  It is also used to seal glass dessicators. 

We sell two products that contain a tube of this grease. Order number 64-0275 is simply a tube of Dow 111 silicone, while order number 64-0378 is a kit which includes a tube of Dow 111, artists brushes for precise grease application, and palletes.