Myself and a few other people got bad parts off Ebay, I have heard the same is happening on Amazon. It is claimed Rock Auto is a drop shipper, not having the problems of others and I am not reading any issues with them.
I would prefer to buy the parts from GM and pick up at the dealer but the springs are $600 with free shipping. The shipping to Ft Myers FL is $48.99 with RA.
Marcopolo did a great thread I have revisited it several times.
https://parts.gmparts.com/product/a...8943559586&showVehicleSelector=true&year=2001
Yeah, ebay is a pretty sleazy place for a lot of stuff, including auto parts and such. Lots of issues there.
Rock Auto is completely a drop shipper, and beyond that you are only getting relayed what the sellers description is of the product,which can be good or bad, based on my experience with them. The worst one lately was on a fuel pump/sending unit assembly that was listed as a topline, and out of production, brand for the particular application. What I got was a super cheapo knockoff product. The vendor on it a closeout mass product buyer and not very careful of their descriptions, it appears, and who feels it is OK the substitute anything that they have and fits no matter what quality level. After sending RA lots of pix of the unit received and of their own listing and waiting a couple of months, RA did issue credit finally. I think they were waiting for the the vendor to credit them.
Of course similar can happen on Amazon or any other online vendor as very many of the them dropship lots of the the things they are selling so they don't have to carry any inventory.
The surer thing is certainly the dealer, but they sure do know how to charge for the parts, but be aware that they also may give you and aftermarket equivalent part once they run out of the OEM version, even if the P/N is still the same. The AC Delco starters, alternators, and AC compressors for my 96 Buick all came through being Chinese aftermarket parts carrying the original P/N. That Buick if in the same timeframe as your van and I guess it is better, I guess, to be able to at least be able to get replacement parts, rather than being not available, but I worry about reliability. My guess is that the dealer parts are the Moog springs in your case, as they normally don't have original coils that old as there are too many variations and inventory costs money. They sell them off to resellers in most cases to reduce carried inventory costs.