[VVTi]

Depending on the age, the later style link arms can be turned around so they stay on. You'll need a pair of decent pliers (ideally pump pliers so the grip is parallel) to force it on.

When mine went this is what I ended up doing and had no more issues. Is seems the ball joint gets warn and the little recess on the arm is not thick enough to hold it on, but if you reverse it with the larger collar holds it nicely and the reverse angle of the arm doesn't seem to affect operation - it probably puts more stress on the arm but at £3 a pop its worth ago - not that mine ever went again (10k miles).

Also when the arm was not connected I didn't notice any performance difference, but in the cold weather did take longer to heat up.