Ok, my DM6 has a leak coming from the on off beneath the barrel. I don't think its a case of a leaky O Ring or anything, as when I twist it hard into place, it doesn't leak, but if I knock it during play or whatever then there's a small hissing leak. Any idea how I can stop this? I know some people lock their on/off's in place? Is that recommendable and how is it done?