To be fair to Happy Valley they seem to have been alright with their maintenance in my experience. Especially on the wood coasters. Fireball and The Dragons have both had large sections retracked.. None of the rides I've ridden at the Happy Valleys ive been to (Beijing, Shanghai, Tianjin, Wuhan and Shenzhen) seemed to be poorly maintained. The second time i visited Shanghai Fireball was running even better than the first time.
I know the SLC at Beijings Happy Valley had some issues though. Although it sounds like it may have been Vekomas fault.
The smaller class of parks are another matter entirely. I saw a mechanic run into the ride area of Shenzhou Coaster in Beijing, collect a small piece of the train and run back to bolt it back on.
If you want some nighmares theres a lovely site with a list of failed inspections and reports.http://chinaridesafety.org.cn/tag.php?tag=%E8%BF%87%E5%B1%B1%E8%BD%A6
With a translator it makes for some interesting reading.