Time to get some new nozzles made?

[SteveW]

If parts appear to be slipping I'd be inclined to look at more suction (bigger hole, or at least tapered).

Flattening the bottom surface on a bit of (wet) wet&dry seems to make it better for a month - and yeah, making sure there's no solder paste in there from a mis-place (or pasting fiducials...) is always worthwhile.
I'm always wary of embiggening the hole, though. If I had more nozzles, I'd probably be braver...

I'd still be interested in glass-loaded. It just feels like a good thing...

[Mike]

The original drawings say Actal, which is fairly slippery - you want it slippy so parts don't stick, and also not liable to build up static, again to prevent sticking

I'm not convinced - if the solderpaste doesn't grab the component enough to get it off the nozzle (which it has to anyway, to beat the decaying vacuum - placing onto a dry board fails), I think I'd like to know about it.
I'd fund getting (some of) mine made out of , say, glass filled nylon, for research purposes...

I've seen sticking a couple of times- occasionally when the board was a bit warped so it didn't quit hit the paste full-on, but most severely when placing power LEDs with soft lenses - in the latter case I had to spray dry film lubricant (ptfe) on the tip before every panel. If I were doing it again I'd make a PTFE insert. I've read that sticky LEDs are a known issue among the bigger guys, and some sell special nozzles - not sure if they use PTFE and/or blow-off.   
The other thing to watch is when using double-sided sticky film to do trial runs, and it covers a fid when measuring board height - the tool can pick up some sticky.   

[phonoplug]

I've read that sticky LEDs are a known issue among the bigger guys, and some sell special nozzles - not sure if they use PTFE and/or blow-off.

If you have blow-off the problem of stickiness of LED lenses disappears. The reason they have special tools is to save picking on the lens at all - not because its sticky but because its easily damaged and should not be picked on in the first place. The tool is specific to an LED  package, and has a recess that the lens fits into so that the vacuum actually picks up on the substrate around the lens.

Best thing you can do with an RV is increase the placement delay. I have it set to 1.5 seconds for one LED package (5050) and make sure I use a tool without the tiny o-ring at the end removed. Places them fine now.