should any sealant be used on the rubber seal? I jammed a new one in and it leaks

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Dog Food! Most kids like it more than Broccoli.

I've only ever fitted them dry. I don't think there was any sealant used from the factory. What I have noticed though is that they are a prime place for rust and that would make it leak.

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I found a smear of rubber grease helps fitment, and it won't harm the rubber.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I had this problem a few weeks ago and luckily the tank was not full
I had fitted a new rubber and new sender and it was leaking
I removed both and made sure the surface in the tank was clean and I also knocked the tabs, that the sealing ring press against, up so the we're more vertical so the sealing ring was able to clamp down tight onto the sender. I think this was the problem because when I tried to clamp tighten the sealing ring it "popped" out from one of the tabs and I suddenly had a bigger leak than original :shock :
So far all good now

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1969 Cooper "S"
1967 Mini Deluxe
1973 Clubman Van (the fleet spare)
1978 ex 1275 LS ("Wizard" Eaton Supercharged)
2015 HSV GenF GTS(occasional drive & tow car)
2019 MINI F55 Cooper S