For a Hypro D503 Repair Kit, see Related Products. Our repair kit is more extensive than the standard Hypro repair kit because it includes the diaphragms and valves. This basically combines 2 of the Hypro repair kits, 9910-KIT1881 & 9910-KIT1987. See Related Products for a link to buy the repair kit.
If your Hypro D503 has milky grey oil (you can see this in the oil sight glass) that means that at least on of your diaphragm has been torn or pulled out of place. This repair will solve that problem. You will also need to clean out all of the contaminated oil out of the crankcase and replace it with SAE 30 oil. That is 30 weight non-detergent oil found at most hardware stores and automotive stores.
It is recommended that you replace all the diaphragms at the same time.
The boxed area of the diagram pictures the latest oil sight glass for the D503 by Hypro, including the black oil sight glass cap number 9910-1040322 and the larger capacity oil sight glass number 9910-1040310. Some years ago the D503 pump was equipped with the same oil sight glass and cap as the D30, being 9910-550030 and 9910-550056. If you need parts for this older version click over to the D30 diagram here and choose the parts from that list.