Late to the scene, but something I mentioned in another thread:
You can buy large diameter silicone rubber "O" rings to fit over the rear of lens bodies before you fit them to the camera bodies - as long as they are a reasonably snug fit on the lens bodies then they contract nicely over the joint between the lens and the bodies and help to stop water from getting in via that route.
Dirt cheap - paid about 99p for 4-5 from China quite recently, and some are always in my camera bags (Lowepro Hatchpack 22 AW or 350AW as appropriate to the day) when the weather looks "uncertain"