I would value your signs in the range $500-800 each.The motor oil version appears to be in somewhat better condition, however, there do appear to be some pinholes or extra drill-holes (better pics would help). I've seen really nice examples of these go for over $1500 at auction recently.
IMO the ebay example you mentioned for $800 is priced way too high due to its poor condition. And of course the asking price doesn't mean much on ebay.
Now that the weather is cooler I'll get in there and take them down.
If I understand both of you correctly; there's no advantage to keeping them together, other than they look good together (in my opinion).