The Hypro diaphragm repair kit 9910-Kit2423 is used to replace worn or damaged diaphragms on the Hypro D403 diaphragm pump. When the fluid in the oil sight glass turns a milky gray color it means that one (or more) of the diaphragms has ruptured and the fluid to be pumped is mixing with the oil in the crank case. If this happens to your D403, you will need to purchase the diaphragm repair kit Kit2423. Fits D303,D303GRGI,D403,D403GRGI