If it's a narrow tank and the float points toward the side there may not be enough clearance between the sending unit and the side of the tank to allow the float arm to travel the full distance. I'm assuming that's the problem sleeve is having. If that is the case the sending unit could probably be turned 90 deg. but that would require some hole filling, re-drilling and tapping since the unit only mounts one way. The other side of that coin is I don't see how the original would work either unless it's made to allow the float arm to travel in the wide portion of the tank. You have any pics sleeve?

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