I just use clean motor oil. The downside is possibly tearing an o-ring pressing the injectors down into their sockets in the intake if no lube is used. I have Mototron injectors (60lbs), and their spec sheet says to use oil and not silicone as it tends to swell the o-rings. They have a link online, in PDF format. I can post the link later when I get home if you like.
