Although the swirl flaps should be the revised ones in my LCI 535d, I decided to proactively replace them rather than taking the risk of one letting go. I got a blanking plate kit from PMW Ltd ( https://www.pmwltd.co.uk/swirl-flaps ) along with new manifold gaskets and o-rings. They are pretty straightforward to fit if you just take your time and follow the instructions.

Since the intake manifold was off, I took the opportunity to replace all the braided rubber vacuum hoses which are otherwise very difficult to reach. The old hoses are quite hard and the best way to remove them from the various nipples Is to cut the hose near the nipple and peel it off rather than trying to pull it off with force.

I also took the opportunity to thoroughly clean the manifold and checked it carefully for any signs of cracks or other damage.

In the end, my swirl flaps were all intact and looked like they would probably be fine for another 50k miles or so, but I decided to remove them anyway. I noticed no difference in drivability of the car or fuel consumption afterwards.