Yeah you need that. National makes the right size o-ring for it if your in a pinch and have a hardware near you that supplies National.

The O-RING store. Vitron, much better and cheaper
16 x 146 V75 Viton® Fluorocarbon Black O-rings (V75146) = $9.12
Larry

i agree that it is not needed but i always use it anyway.

I got mine at McMaster Car also, like Rob posted


McMaster # 9396K166 is high temp (red) silicone @ $0.67 each
McMaster # 9452K153 is OEM style Buna @ $0.16 each

Thanks. I hate to buy merc when its available aftermarket.