Having learnt the intricacies of this forum's search facility and read literally hundreds of the archived posts to find the references you give, I'm now off to the garage armed with info on everything from the 'Herr Fuch Finger Test' to the 'Updated check valve' in the oil filter housing!
(Along the way I have also learnt that the 'little electric motor' that accidentally became detached when satnav kit was fitted above passenger footwell (RHD car) does actually have an important function!! My [now internationally renowned!] mechanic thought it might be blowing air into the door skins to prevent corrosion!)
I will instruct that the preload be checked (assuming he can borrow the appropriate tool) and see where we go from there. Could someone tell me the checking procedure? Is it performed with the engine warm / Compensator Elements pressurised?
With many thanks.