Mini Cooper Engine Mount Mystery



I have a 2005 Mini Cooper S with an automatic transmission (my first automatic in a toy car, had to have the paddle shifters to Schumacher around town?). The upper passenger side hydraulic motor mount went bad at about 2 years / 15k miles and was replaced with a new and improved mount under warranty. A few months ago, immediately after the dealer replaced the oxygen sensor, the ?new? mount started making noise and hydraulic fluid was leaking from it. I decided to try a different solution, and purchased an after-market solid (non-hydraulic) mount. I installed it and the car exhibited a lot of vibration (especially at low rpm) and the performance at low rpm also was severely affected. When you accelerated, the car did not get up and go, but struggled. I did not see the yellow engine control light come on, or see any other error messages?

I loosened up the aftermarket mount, assured the support arm was aligned correctly, and there was no change or improvement. I checked the other mounts and they appear to be in excellent condition. I contacted the aftermarket mount manufacturer who said there were only a few owners who complained about vibration. I then decided to put the leaky mount back on, and voila, the vibration is gone and the performance is back to normal. This made/makes no sense to me. Also strange is the noise (an intermittent ?clunk/click?) on acceleration/deceleration attributed to the mount is gone too (recall the second mount was wet with hydraulic fluid from a leak). My fairly far-fetched speculations are something in the electronic engine control system that did not like the vibration, and/or the few wires with a support on the forward/outer bolt on the mount tower have been impacted. I did not undo any of these wires, just pulled them to the side. But they were moved and jostled some in the mount switch process. I have not investigated exactly what systems those wires are associated. Any ideas on why a solid mount could affect performance?

Thanks for any ideas! Cheers, John