I had a similar experience to Malcy, with a Charnwood planer/thicknesser. The machine was impossible to maintain accurately because the top outfeed table was set a a very slight angle to the infeed. When I discussed this with Charnwood, they told me to slacken off the table's securing screws and adjust the table, but I pointed out to them that it was fixed in position with dowels.....so they said to ditch the dowels. I did as they suggested, and now i have top adjust the outfeed table every time I use the blessed thing (thankfully, that's a rare ocurrence).
Les