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Generally, a bench seat in a boat like this, will last 70 years or more, or until the boat is destroyed somehow.
Why would a company keep a warehouse full of seats it would never sell?
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Why wouldn't they? They're still building the same boat the OP has, I've got both a 1999 and a 2011 model 14SF sitting here, both hulls are identical, (same as catalog pic the OP posted prior).
I don't see why a manufacturer, who is located right here in the USA, wouldn't be able to pull a seat stamping from the factory and sell it as a replacement part. They are the same on that model, given a particular seat position.
If he had a really older model, in which the seats are quite different then I could see your point but the boats coming off the line today are the same as his.
The same goes for the boat corners, I've been able to buy replacement parts myself for Lowe, Grumman, Mirrocraft, G3, and various others, I don't see why Starcraft would be any different. Those corners are basically the same and can be interchanged from about 1958 or so till the current models. ( I know for a fact that the corners on my 1960 Seafarer are the same as those on my 1977, and those will interchange with the newer models as well. The star disappeared from the casting about 20 to 25 years ago. About that same time they made that casting slightly bigger, the newer version is about 1/2" larger overall but fits just the same. Its also not a Starcraft only casting, I've seen those on a few other brands, including earlier model Sea Nymph, Lowe, and Grumman models from the mid 80's to mid 90's or so. Possibly they all bought the corner castings from the same source? This would explain the loss of the Star casting and the new oversized universal type casting in the later years.
I'm not sure how many salvage yards would hold onto an aluminum hull like that, there's just not much to take off it and its worth more in scrap to them then parts in most cases. Every hull that I've ever scrapped, got chunked up in a shredder minutes after I hauled it to the scrap yard.
I did check but I've got no spare caps here like yours but there has to be an old time Starcraft dealer somewhere with a few on a shelf either new or used. No doubt they have to be available just in case one was damaged in shipping, they're certainly not going to scrap a new hull over a broken corner casting or handle.
The last I heard, Starcraft was back under family ownership, which included Smokercraft, which is apparently the main company these days. Sylvan is also in this group. My guess would be that any contact would have to be through Smoker Craft, try the contact us link at the Smoker Craft webpage.
The last contact info I have for Starcraft Marine is68143 Clunette Street New Paris, IN 46553 Phone number: 866-772-4538 or see their contact page at
http://www.thebestboatbrands.com/contact.php