It probably has an old drive belt, which might contribute to vibration. You might try changing it out for a a flexible link belt. You buy a length and then assemble it to exact length. I also think the lubrication is a big factor. My Laguna TS doesn't have a height lock and it is rock steady. The Laguna TS takes a slight effort to crank up but has a large, heavy wheel that reduces the effort needed to turn it. I think I'd also clean out the grease, particularly if the slipping increased or began after adding the grease fittings. Grease and TS mechanical parts don't mix well.
The more I do, the less I accomplish.