I bought one from Cycle X.
One insert fell off direct when it got a bolt inside before tightening it. Happened this weekend. The threads were completely destroyed from the very begining, Loctite only held in it place. I ordered it 6 months ago, so it's too late and too far away for complaints returning the valve cover. I ordered new tach gear to have a complete unit.
The overall quality was really bad. Old dirty oil residues inside I had to clean and brush, threads for tacho cable locking bolt completely off. I upgraded to M6 with a tap that I could use direct.
Maybe I'm happy that the bad quality was vsible direct instead of risk getting metal flakes and oil all over the engine.
My old cover went on after I had checked for alu flakes on rocker arms/cam holder and my new cam. All alu flakes went outside only
I'll weld all 8 inserts when I do not trust the glued threaded inserts. There is alu repair that I think will work.
Like this:
http://www.alumiweld.com/Find welded cover, pay more for correct quality and avoid problems is my experience.