Clattery when cold
Join Date: Feb 2012
Location: United Kingdom
County: Greater London
Powerflex are polyurethane, OE are rubber. Urethane is OK with petroleum grease but rubber definitely isn't. I am copper grease's biggest fan, specially on AR quick-corroding fasteners, but it'll just destroy rubber.
You can buy (Castrol) red grease specially designed for rubber bushes, brake and hydraulic parts etc, which is vegetable-oil based. I've never seen it as an aerosol, only in pots and sachets.
Silicone is fine for either type and available as an aerosol, diluted with glycols (also rubber safe, cf antifreeze) to be thin and have good capillary pull into the joints. It's not as good as a grease as rubber grease, but it doesn't need the joint dismantling to use it.