Try Fluorocarbon (Viton) O rings; any air con place should stock them. I think Ford switched to them too. These O RING SEAL AIR CON CONDENSER EVAPORATOR POWER STEERING FORD AU (5) GENUINE | eBay Also be extremely careful to use a spanner or socket to gently screw the power steering switch in; turning firmly by hand using the body of the switch will often cause a small fracture and leak in the plastic or between the plastic and metal parts of the switch. Comparing the Viton with Polyacrylic here Polyacrylate (ACM) O-Rings | ESP International suggest the Viton meets or out performs the ployacrylic in most ways. Also see Polyacrylate (ACM) O-Rings | ESP International and Chemical Resistant Fluorocarbon (FKM) O-Rings | ESP International . As I recall due to their better compression resistance (see Material Choice Guide to Selecting Rubber Compounds ) and worse cold flexibility, the Viton ones need to tightened slightly more that the polacrylic to seal and that increases the risk of fracturing the switch; they are less squishy to put it simply.