The platter is supported by the ball bearing and thrust plate assembly.  This is the bearing from an L70, check out the plastic end cap.  The original was missing but this top from an after shave bottle fits perfectly. :-)

Centre front is the steel thrust plate and to the right a thin plate that goes between the steel and the ball bearing.  I'm not too sure what this thin plate is made from, but assume it is some form of hard nylon and is there to reduce friction and noise.  Any info would be appreciated - please email. 

After 30 years of supporting the weight of the platter these parts can get 'dimpled'.  Just turn 'em over and replace for another 30 years of record playing.

Oops! Feb 2005 Update.  Thanks to Stefan who sends this info :-

"This can work but it is incorrect.The nylatron pad is meant to be dimpled and new ones from Technical and General have the dimple pre-stamped into them.The metal thrust plate you could probably turn over."

Btw thrust plates and ball bearings are much discussed for modern turntables.  Afaik Delrin is a favourite material for the thrust plate, and ceramic ball bearings have some better qualities than the plain steel type.  After the introduction of the Linn single point on a hardened thrust pad for their Sondek, there was a school of thought that advocated no materials with 'give' should be used in the bearing.  Such designs would allow micro vertical movements in the platter, a bad thing.

There would seem to be some tweaking opportunties for the Lenco here.  Check out the Audiogon 'despot' thread for posts by Stefanl.  Also searching the Vinyl Asylum for 'thrust plate' returns some useful information.

Imo Lenco knew more about bearings than I do, so the safest way to use the deck is with both plates.  However for the purposes of experiment I think I may try one of my Lencos without the thin plate and let the ball bearing sit direct on the steel plate.  It will need checking regularly for excessive noise and wear, but should allow for interesting comparisons.

G99 on the left, B55 on the right.  Models with the heavy cast alloy platter (G99/L70/L75/L78) used the large bearing and the smaller one is used with the pressed steel platters (B55/L69/L72).  If found in original state, all bearings I have seen so far use grease - as seen on this B55.  My latest deck a mid sixties L70 looked original, but was as dry as a bone, maybe because the plastic end cap was missing.

Compare the B55 and G99 bearings complete, the bearing housing is open ended with a circlip holding in the thrust plate.  The 99 bearing on the right also has a plastic end cap.  If oil is used to lubricate the bearing, it leaks out, so I use grease to pack the housing and oil the shaft to reassemble.

Dismantled - both bearings are of high quality finish with a ball bearing providing near single point contact on the thrust plate.

While they look interchangeable the fixing holes of the 99 bearing do not line up with the 55 plate.  Shame. 

Here is a pic of G99 and B55 deck plates.

This picture shows the differences between the heavy and light platter versions. 

Heavy - speed control on the left, moulded deck plate, large bearing.

Light - speed control on the right, flat deck plate, small bearing.

The bearings look interchangeable, but the fixing holes are slightly different.  The larger bearing could be fitted to a flat deck plate by enlarging or slotting the holes in the plate.  Potential upgrade route? Maybe.