This is the stuff that both Bosco & Olympia use to lubricate the pistons in their lever machines. What's so special about Dow Corning 111? Well it is approved for 'incidental' contact with food (NSF Standard 51 for use in food processing equipment). My interpretation of this US standard is that it is more about ensuring the grease will continue to lubricate the machinery to which it has been applied if the grease is contaminated with food, whereas 'normal' lubricants will often degrade/breakdown and cease to provide adequate lubrication in this situation. It does not mean it is good to eat.
Probably the more relevant standard is that it is also approved for use in situations where it is in contact with water intended for human consumption (NSF Standard 61 for use in potable water applications), which obviously is exactly the situation you have with a lever espresso machine piston.
Dow Corning 111 is described as a general purpose O-ring and valve lubricant. It provides a non-curing moisture barrier; high dielectric strength; moisture and ozone resistance; good thermal, oxidation and chemical stability. It has a heavy consistency and is a translucent white, grease-like silicone paste.
Importantly it has an operating temperature up to 204C.
Where we've found it to be absolute gold is on both cylinder bores (large & small) of the Bacchi. In our view the Bacchi instructions don't really underline the importance of keeping the bores lubricated. To test the health of your Bacchi lift the main piston assembly out of the frame (the engine of the Bacchi if you like), and hold with two hands. Using both thumbs push the piston upwards from the bottom. If it is sticking or binding at any point then it needs some Dow Corning 111 smeared in the thinnest film imaginable on both cylinder bores all the way around, and for the full range of travel. The difference in the smoothness with which the piston in the Bacchi moves after you have undertaken this easiest of maintenance tasks will be like night and day; and so will the taste of your espresso.