I have fitted a new door strap on my 156 and thought id share the process. This is for front drivers side. note straps are universal so can fit either left or right although are specific to front and back.
1. Make sure window is up!
2. Remove door pannel.
Remove screw behind interior door handle
remove speaker grill - 4 bolts to unscrew speaker - disconnect speaker - remove two more screws behind the speaker cone.
Remove bolts within plastic surround for electric windows (under rubber mat) and remove pastic surround as well as disconnecting the window switches.
After this two (10mm) i think) bolts will be exposed - unscrew these.
Now remove the surround which houses the tweeter - and unclip.
Before removing the door car pull off the plastic mount that is oppersite to the wing mirror
Gently prise the door card off. UP and out motion
Being careful not to pull the lock out of place.
Pull back white cover to gain access to inside the door. as little as possible i would suggest.
3. unbolt the old door strap and remove from door. I undid the bolts from the car itself and then the door ... also adapted an some tools to access the other bolts see picture.
4. FEED in new door strap MAKE SURE ITS THE RIGHT WAY.
thread the rubber mount back on and bolt door strap to the door. Loosely
Then the bolts to the car
then tighten them up.
I applied some white grease.
5. then re fit door pannel and plasic surround behind mirror.
NO more knocks !!
When fitting make sure the new door strap is the right way round and fully open. as mine was semi closed - making it impossible to fitt without opening it fully. which took some time.
Overall though its a 20-30 min job max - just dont loose any bolts
Hope this helps... someone
BTW my first how to thread any good??
Apologies for the sideways picture - silly iphone