Hi all,
Some good general principles were laid out above. In general, youre balancing out two parameters against each other: bearing play and damping. Theres no hard and fast rule. In addition to the local parameters within your control (your turntable drive system - motor, controller, drive belt, platter/mass, bearing play), you may have to adjust for the tuning of the rest of your system.
To maintain your sanity, Id focus on the turntable to the exclusion of your downstream components, but I mention them above, mainly to make a point that this all fits together into a coherent whole.
Ive not played with VPIs, but everyone whose opinion I respect, tells me that they have enough play in them to work best with a lightweight lithium grease (think bicycle wheel bearings). At the other extreme, Galibiers, along the vintage Micro Seikis tend to work best with lubricants that are closer to water in viscosity than they are to something like 5W motor oil.
This is where I take issue with the use of thicker oils in my tables oils that can work, but which require a multi-hour seating process. It would be a great thing to build up the Galibier mythology, but it hurts the music.
Bearing play (as youd correctly guess) is mitigated by increasing viscosity, and in general, the less play the better. Damping is a bit more complicated and heres where the listening comes into play (to balance bearing rigidity against over-damping).
The unfortunate reality of all hi-fi components is that you can damp things too much. This is another case of having too much of a good thing. Youll read various threads on how theres nary a person (for example) who uses the silicone damping fluid in the Tri-Planar tonearms. The general consensus is that while an occasional nasty is tamed, it comes at the expense of a fairly ho-hum sound overall.
The same holds true in lubricant choice for turntable bearings, speaker design, and amplification design. Its extremely challenging for example, to filter a power supply to the point where its quiet, but that still has great transient response. The common error with many good amplification components is that they get the quiet part right, but miss the nuance and subtle transient details. Getting to quiet is comparatively easy, but quiet with no sacrifice in musical nuance is a very challenge to pull off.
The good news is that experimentation wont do any harm, and you have a system tuning component available to you. Id advise against staying away from oils with detergents in them. Also, some oils will form a varnish after a while (3-In-One), but even this can be cleaned with something like carburetor cleaner. The synthetic motor oils are fine.
Heres the link to more of my comments on the subject:
http://www.galibierdesign.com/prd_bearing.html.
Cheers,
Thom @ Galibier