And, as I noted in 2023, that NAPA kit seems to be NLA. But do your own checks. You might just get lucky and find one sitting on some NAPA shop's shelves. I just re-checked my old files. The NAPA kit (PN 6601000) was described as a 'RANCO HTR-100' rebuild kit. It was evidently applicable to the heaters used in the Studebaker Avanti, so it's conceivable that it was used across the entire Studebaker line (Lark, Hawk, etc). A little snooping around a Studebaker owners club website might turn up a lead. RANCO appears to have been swallowed up by Robertshaw. Most of the focus for the RANCO product line these days appears to be in electronic temperature controllers used for commercial/industrial heating systems. I suspect that the 'RANCO' of 2025 may be nothing more than a brand name (i.e. it's unlikely you'll find a RANCO factory with a parts desk). Just one thing, though: I see that NAPA Canada lists something called a 'URO Parts Heater Valve Repair Kit'. A little checking indicates that URO Parts is a brand marketed by A.P.A. Industries (Simi Valley, CA). A.P.A. provides aftermarket parts (incl. cooling system parts) for a variety of European, Asian and North American cars and trucks. In their website, they say: "A.P.A. specializes in accurate reproduction parts for classic vehicles, including a wide variety of items that are no longer available from the dealer". Maybe there might be some leads there. The heater control valve design used in the 510 and Z probably wasn't unique to Nissan. In fact, the Nissan heater design bears certain resemblances to the British 'Smiths' unit that was used in so many UK cars back in the 1950's and 60's. A little investigation along these lines might turn up a British shop that specializes in heater restorations and has a back room filled with obscure parts like a little rubber washer that will fit your 510's control valve. Try this link for a starting point... The MG Experience - Smith's Heater Restoration