Bench seat I.D

[Aussie Ol' Blue]

Can some-one identify what year seat this is? I'm suspecting its a Silverado seat but my research hasn't been able to come up with the year. I'd like to find out if the cover is replaceable and available. It has two zips at the back of the upright section and I'm not sure how the base cover is fixed. It's in reasonable nick except for some kind of brown gunk that's been spilled. I think it's some kind of glue and I've tried melting it, it softens but wont let go. Ultimately I would like to get some Buddy seats, but for the time being I have to do with what I've got. Any and all info would be greatly appreciated. Thanks heaps.