Can't get Simon to take tracer fluid and get out of his apartment. I imagine it just gets worse from here on.

As I responded in the other thread:

A hint comes up when you first pick up the tracer fluid (or any interactable object): just left-click when the object is shown in your hand. So you click once to pick up the tracer, then click again to drink it. I just tried it, worked fine.

What happens to you, when holding the tracer, and left-clicking? Not double-clicking or right-clicking, just one click to pick something up, and then another click to use it.