Dual bought PE mainly because of their patents.
Their build quality dropped because they could not compete with Japanese companies and were forced to reduce costs.
A couple of Dual technicians on AudioKarma claim that some PEs are so complex they're practically unrepairable.
I've repaired a couple of fully automatic PEs. Maybe I was lucky but they weren't
that bad. I wouldn't say I fully understood what was going on but I managed to find the cause of the fault... (dried grease) and then take them apart and put them back together again... I don't particularly like working on automatic turntables but at least with the PEs you don't have to worry too much about breaking plastic parts in the process of fault-finding!
OTOH, I must have been feeling brave when I did them, my Dual 1019 is still sitting on the shelf waiting for me to finish fixing it...
Re Japanese competition, well, yeah, the Japanese did pretty much beat Dual at their own game. Not as badly as Garrard though! IMO as lovely as these old German decks are they could all be accused of being both over complicated and over engineered. Even a Dual 505 is unnecessarily complicated compared to say a PL12D... With the older models that's their appeal nowadays, but from where I stand the Japanese did a lot of good in terms of bringing real quality to the masses.
The new generation of (relatively cheap) Dual automatic decks are really awful. It's one thing trying to compete with the Japanese in the 70s, another trying to beat the Chinese at their own game now. They are still 3 times as expensive as the equivalent Chinese made Pioneer or Audio Technica... and the Chinese decks are more reliable.