Henry, firstly thanks for your post. If a lift is shaking parts of a controller, something is seriously wrong, most likely mechanically. Do you feel like the vibration is coming thru the floor of the car? Or is in the machine directly above the hoist machine? Does replacing the contacts on the controller fix this?Either way, it can lead to a catastrophic failure, particularly if its the lifting machine ie a failure of input shaft into the gearbox(geared machine), which can lead to a unintended lift movement.

Think of the controller parts as a secondary issue, so try to figure out the vibration. I would go over the whole mechanical set up if it was me.

But it still comes down to the issue of age. When you purchase a building, you would have to plan for obsolescence costs, as part of the management planning. It comes hand in hand with rental fees that you generate. I understand it isn't as simple as that sometimes, but it your responsibility. Think of it like this, the best building provide its customers with the best environment, the best relationship with each other, within the confines of the pricing structure. That means, on the flip side, that if you customers are scared to travel in the lifts, then they may decide they want to move to another building, and then you lose revenue. Even if use the whole building yourself, think of it as capital works, which can increase the value of the structure and its future sell price. Even if you staggered the upgrade( I would go a MRL type lift as a complete upgrade) with the bad lift first, it is the way to go.