I've ridden many a Century in the rain. The Original TOSRV is known for it! If it doesn't rain on Saturday's 105 miles, the chances are you'll get it on the 105-mile return on Sunday!
If I ever ride any distance in the rain, the chain gets sprayed with WD40 to remove water (WD40 = Water Displacement 40th attempt) then regular chain lube applied. Never had the grease 'wash out' of wheel- headset- or crankset bearings. I use 'Waterproof grease' aka boat trailer axle grease on those bearings for exactly that reason.
__________________
'75 Fuji S-10S bought new, 52k+ miles and still going!
'84 Univega Gran Tourismo
'84 Univega Viva Sport
'86 Miyata 710
'90 Schwinn Woodlands
Unknown brand MTB of questionable lineage aka 'Mutt Trail Bike'
Plus or minus a few others from time-to-time