If the keyboard was balky from day one it's probably more because the keycaps and/or key posts are slightly bent, out of spec, or misaligned
. That or the wells which they pass through are deformed or improperly manufactured. Lubrication won't fix that, and could possibly seep into things and cause additional problems down the line.
Whatever you use, just be sure it doesn't dissolve whatever they're using for the membrane or other contacts in the keyboard. The problem with that
, however, is it usually won't happen right away. Some solvents and lubricants can take weeks or months before you experience a problem from them eating into or softening/hardening something enough to cause a failure.
For cleaning sticky contacts and keys, you could try a non-residue
foaming contact cleaner available at Radio shack or an electronics supply store. But I'd be careful even with that.
When in doubt, compressed air - or a 1-hour soak in distilled water, followed by a careful "blow out" with some compressed air, followed by a three or four day air dry
- is still your safest and best bet. If that doesn't fix it, I'd suggest (as others have) you cut your losses and get a new keyboard if at all possible.