I bought a Wingsung 699 recently from AliExpress because I wanted to try out a vacuum filler. Ink leaks from around the nib whenever I cap it, leading to ink getting on the grip. When I write, blobs of ink sometimes burp out onto the page. Is this typical for this brand? I have another no name Wingsung (I think it's actually a knockoff of the Hongdian dark forest) that has no issues.
Quality of knock-off brands like Jinhao and Wing Sung is going to be pretty universally shit. You can usually buy a handful and one will be at least decent though.
One thing you could check - any moisture present in the cap can tend to draw more moisture out of the pen. You could dry rinsing and then thoroughly drying (Q-tip, compressed air, whatever) the inside of the cap, dab the section and nib to make sure it's fully clean, let it dry for a bit (you can shield the nib from air with a cloth to keep it from fully drying out) and then try writing with it and capping it again to see if it sorts itself. If not it might just be way too wet and dumping ink in the cap, or you're knocking the pen around too much causing ink to leak from the feed. This is all of course assuming it's otherwise properly tuned.
Hmm, that's not been my experience. I have probably 15ish pens from Jinhao and Wing Sung, and only one had a (minor) QC problem. They write well, for the price, and you certainly don't need to buy a handful to get a single good one (at least of the ones I've gotten). Sure, you should be prepared for the possibility that you might get a lemon, but I do think that that's the exception, not the rule (at least these days).
That's just not true. I have 35 Jinhao's, and ~25 from other Chinese brands like Moonman/Majohn, Wing Sung, Hongdian, Lemon, Asvine, Kaigelu, & more. Out of all of them, only 2 have been duds; one was a Kaigelu which had a bad nib that I was later able to fix, and the other from a no-name gamble which was horribly unbalanced because they added brass to the finials to make it feel more substantial. The nib was pretty decent though, and it at least looked pretty. Everything else has been fine to excellent. Are they all going to be 5 stars? Of course not, but considering the majority of them were under £20, and around 75% of those were under £10, they've been great. Definitely no worse than Lamy, Kaweco, or any other western brand in that price point. The more expensive ones have all been fantastic.
Granted, there are still some that aren't good and should be largely avoided. Generally, pens that you can't find a brand name for will always be a gamble, as are the 4-digit model number Wing Sung's. They're a different company than the 3-digit ones and I've only ever heard bad experiences about them. But on the whole, Chinese pens have come a long way. Don't be so quick to dismiss them completely.
Drying out the cap was a good call. I think reseating the nib was what did the trick, but thanks for the suggestion!