I'd trust the D51R recommendation. I have one on order from Interstate but will not see it for at least a few days as it is a new acount setup. This distributor didn't handle the Optimas a few years back so I was referred to another who was always slow, and unresponsive. We did have a nice delivery deal where he'd drop at my Baldwin Filters distributor and then they'd come with my filters delivery every other week. Now I can get them delivered to my door on the reglar route.