I have spent some time on this project today. Purolator still makes a P-51 or L-20051. The ones I have are 4-3/4" high by 4" in diameter. I checked two Pep Boys and they did not have any in stock. Amazon shows them available, however they have different dimension on them. You might want to order one and see what size they actually are since I find it hard to believe the same number would continue with a size change. Seems odd to me, but what do I know. If they are wrong, Amazon takes stuff back with no problem. I did find a few on eBay with that are the size mine are. Advance Auto Parts stores say they carry them. I have cross referenced until I totally ran out of any type of number. Finally, I will say that am surprised. Five years ago Pep Boys had them at the two stores I went to today and another which I haven't been to but will check when I get a chance. At that time they always had three or four in stock. Strange.
