I got in a discussion on linked-in about my early cgriatmas present to myself (my HS400)--the discussion broadened as they do on that forum and a couple of fellows in the RV industry got invilved. They said it was well known in the "industry" that Chongqing Huansong Science and Technology Industrial Co., Ltd. (Hisun) dumped Massimo in 2018--having become fed up with their poor quality control and customer service.
Your experience with them bears out Hisun's concerns, and the EPAdata (see a clip below) illustrates Massimo's marketing of Chongqing Huansong (Hisun) manufactured vehicle from 2010 through 2018--when they abruptly switched to a variety (four to be specific) of other Chinese and makers--selected I am sure by cost, not quality.
Massimo likes to bill itself as a "builder" (implying "manufacturer") of recreational vehicles--however in reality they are an assembler and vendor of kits they buy from various manufacturers; they assemble as required and carefully place their brand stickers on the stuff they slap together.. They do not "make" anything any more than I "made" Mr. Machine when I was seven.
I would not have expected installation of parking brake pads to be part of Massimo's assembling the vehicle, but who knows, they may have saved 50¢per unit by buying them very completely disassembled--or maybe Hisun screwed up. My HS400 is vert well made, green paint daubs on everything that had to be installed/torqued.
Last Fall my daughter bought a "some assembly required" 4' x 8' Folding utility trailer from Harbor Freight--what she got was two large boxes, one containingthe axle and wheels, the other containing steel panels and angle iron--AND a 25 lb. plastic bag of 893 million nuts & bolts.
Fortunately the grand-kid was there to help the geezer. I never before thought I could get tired of screwing--"some assembly required" my backside...