Hi All. I thought I would share what I did on my 2018 171, and hopefully it was the right thing.
Problem: Fan vent corners lifted up, cracks, was leaking into shower. Roof/plumbing vent cracks. Bubbles in in sealant around antenna, fan and vent. Rear wing had some light cracks. Overall the sealant still had adhesion to the roof and was gummy when picked at.
Solution:
1. I cleaned the existing sealant as well as I could, it was pretty dirty, with Denatured Alcohol. This was the worst and most time consuming part.
2. I put in about 8 more crews in the corners of the fan vent to keep the corners down. I put a screw in between each of the existing screws around the plumbing vent. I lightly checked/tightened all existing screws.
2. I put grey dicor (which seemed to match perfectly) around all corners (even if they were not cracked) and over each screw head.
Thoughts:
1. The dicor does not level as much as you think. It smooths out, but doesn't get real flat, at least it as not after 1 hour. So when patching, it is hard to make it look nice.
2. I looked at all the other seams on the rpod, which look like mostly clear or black silicon, and they all looked ok, but they were all very dirty. Denatured alcohol cleans them up a bit, but wasn't ready to start doing that.
3. Under the rear wing silicon is in the worst shape. I am not sure if I should bother fixing this.