I never thought I'd see this, but it looks like Land Rover officially specify a water leak as standard:
QUOTE
4.2 VEHICLE BODYWORK
It is important that the standard of the Converter’s bodywork be comparable
with that supplied by Land Rover. The Converter shall leave the bodywork as
supplied intact to retain the structural integrity of the vehicle.
Should the base vehicle structure be changed then it may be necessary to
revalidate certain areas of the vehicle, such as seat and seat belt mountings,
cab strength, water leak, wind noise, vibration, legalities etc. and as such this
should be avoided.