Just so you know, the ball sold for $2270 including the buyer's premium in the Heritage Auction last week so the Ebay seller is likely to take a reasonable offer possibly less than $4K.
I think you can do a lot better for $5K so I would keep looking but I wouldn't be too worried about the authenticity. Two experts in the field of autographs have examined this ball with all their bells and whistles and agree it is authentic.
You can sell an item with PSA/DNA and JSA LOAs at any time you wish through any major auction house if you ever decide to.
Who knows if that will be the case 20 years from now but it has been the case for the last 10 years or so and currently would be accepted without any further endorsement.
If you want more iron clad proof of authenticity, I would go with a Ruth check encapsulated by PSA/DNA that you can get for about $4-5K. Authenticated checks are not all that rare but give the owner additional confidence in the authenticity. Just be careful because there are check forgeries out there as well.
I personally don't like the Ruth but I looked the certification # up on the JSA web site and it is legitimate. Spence had the ball in hand so I would trust his opinion over mine.
It is worth a lot more than it sold for. I would say $5000 or so. I recognize who bought the ball and he is also very knowledgeable of Ruth and Gehrig and obviously had two higher ceiling bids to protect his interest in the ball.
It will likely show up in an auction house over the coming months.
I think both signatures look strange, but obviously JSA knows more than I do. There are certainly better examples out there.