Steven, if you search these pages back a few weeks you will see that Chris Tilley from South Wales had a similar problem. I have also had the same problem as had one of my local chums. The solution was that I designed a part which fits between the top of the lower guide and the bottom of the top guide and this prevents the lower valve guide from ever starting to work itself loose. I sent drawings to Chris and he got a local machinist to make two very nice items which also allowed him to use the oil seal on top of the lower guide. I am prepared to get a batch of these made if the interest is there and although the two I had made originally were made of steel I would probably use 7075 aluminium alloy for these as it has proved its worth and strength in the aluminium John Emmanuel steering heads I have had made. It will have to be a batch. The reason is that the chaps who do the CNC work for me do not really want to make less than ten off of any item. When I try to get one (or four offs) I run into trouble with people fitting the work in. E.G. I have been waiting eight weeks for some minor stainless steel parts to be made to fit an alternator kit to an open 'D'. Have a look at the Chris Tilley correspondence, which does include a drawing so you can make your own if you have the skills, and then let us see whether there is enough interest to make it possible to get a batch made.