That is usually not the reason for an oily residue. It is however a number of things. If using the Alumilite Regular (found in most starter and refill kits), it may have not been shaken well as the B side seperates after setting and must be shaken prior to use. Another possibility is that it is not measured to the appropriate mix ratio. Alumilite resins are all a 1:1 mixture. Some are by both volume or weight however the Clear, Flex, and Filled systems are only 1:1 by weight. DO NOT alter ratios in hopes of changing pot life or hardness. This does not work. The last and most often issue is the material was not thoroughly mixed. This is most prevelant when most of the piece is hard but there are noticeable swirls and soft areas on the surface of the part. The A must be blended well with B components for a complete chemical crosslink to take place for a full and uniform cure, leaving nothing to leech. Scraping the sides and bottom are crucial steps in mixing the resin thoroughly and avoiding soft spots or unmixed areas that remain wet.