Believe me your experience with the 8324 is atypical. I run one on my line and its the both the highest syncing and most stable I have tried, out of many.
If you have been put off zyxel modems (understandably so) then for cheap you could try a Billion 8800NL v1 next. I have one and it was super stable, the modem code it uses did not exhibit the strange bug with vectoring, and just a bit lower sync than the zyxels.
Edit: 2 on the auction site for around £25 atm, can be had cheaper if you wait, but they are there.
I'd add that the Billion uses the same BCM63168 chipset that makes the zyxels good and is only missing the nice noise filter on the line input.