I used plain old wheel grease on mine over three years ago, have had them apart several times, no evidence of deterioration of the urethane, If you are concerned about it use a silicone based grease.

 

I was referring to "technical vaseline grease" that is chemically neutral and stable in time. It was used in washing m/c timers where plastic and metal parts had to coexist.
Urethane has excellent resistance to petroleum based greases but will not last as long if it comes in contact with alcohol; so you shouldn't use today's gasoline to clean your parts...
I live far from the sea, so I use 'Molykote' grease for parts exposed to sunlight, rain water, dust+friction and Lithium grease for the more delicate assemblies.

 

I know it's late in this thread, but for others who might come across it at a later date:

I come from a professional cycling background (mt. bike) and years ago we were told NEVER to USE LITHIUM greases anywhere on our bikes because of it's tendency to react with certain plastics and rubbers.

Silicone-based or synthetics that are NOT lithium-based are best. I think our mechanics even used synthetic electrical grease sometimes. Not sure why. One thing I know is that they were always in touch with our sponsors' tech depts. and our manufacturers' tech people. These mechanics worked for a 6-time world champion (not me), a Pan-Am champion (not me), and a 2-time national champion (again, not me). They didn't make mistakes, ever... not even with something that seemed as petty as choice of grease or lube.

 

i used plain old wheel bearing grease, no problems so far...