Would be great to know more about your first hand experiences, especially what hasn't held up well. I started a rather controversial
post on the W114/5 Facebook group to try and capture this.
Sadly, my garage has shuttered due to COVID-19. We were waiting for rear shock absorber sleeves. These were not supplied with the rear Bilstein HD struts (only with the front), nor equipped on the standard spec car, but were available from the factory for the Heavy Duty option. Rear bump stops from Stuttgart too. Remarkably, both still available and very useful over the long haul of ownership.