Hi Ian That looks to be a nice clean example of a 981. It should clean up well. Once again, I can only stress to be careful when cleaning the nickel on the hood. I don't know what went wrong for Primus with these tops (and sometimes the globe cage as well). I suspect they outsourced production of them and the nickel quality is not what you would expect from Primus. I would not remove the vapouriser block from the tank. They are fitted and soldered in at the factory and are not meant to come out again. The fuel pickup is just a straight tube that is in line with the opening at the top. If there is a blockage it is just a matter of pushing a sharp screwdriver or similar all the way through. Jets and needles from the 991 can be used on these, so spares are available. I have seen examples of these where the top is just held on with the screw put in from the top and a plain nut on the inside. Maybe they ran out of top nuts at one point and just wanted to complete the order.