No argument against OEM but I got my Dak used and it came with a locking cap that failed, when it retired I was carrying two mortgages while I fixed up the old place so $ was tight, I got this August 2016 and it's kept on keeping on ever since: Clearly I'm not the only happy purchaser since it's got over 1,000 reviews and has 4.5 stars.

 

I had the same issue with the fuel cap, but I was in my small town and low on funds to fix it. So usually if the cap is loose or the gas cap seat to filler neck is worn. You can take off the o-ring and just put a gasket 1/16" thick to fit on before the o-ring, and reinstall the o-ring.
I did that and I have never had an issue since.