Kiwi valve covers are the best you can buy. I make these with an expensive, high-quality silicone O-ring (not cheap black neoprene) for high heat resistance (near exhaust) and will not settle and leak over time.
Note: Sold individually, 4 required
Note: Valve covers can be retrofitted to 1935-38 models, but they require the use of 41814 threaded (1939-53 models) pushrod guides. This ensures a completely leak-free valve train.