Nick: I would not do any additional trimming of the antenna, just scan up and down with frequency then see where it falls in.
Then report, you may find it never gets exactly there but gives a reference point to where the rise and fall of the reactance occurs. The antenna is VERY close.
However, you may see a rise in VSWR where the X=0 occurs, (very common) it's just a good point of reference to where X=0 and Z=R fall together.
I also understand why the whip was so problematic, seeing it's true condition (I was assuming it was a new install) my bad.
I have not used the product suggested, but seeing the experience of Slowmover, I believe it sounds reasonable to do the cleanup job intended.
I have used a similar "food grade" stainless polish in the past with a brass wire brush to do the job. (I had a supply available so I used it). I would look for a set-screw and remove the whip from the stud coupling (if possible) and clean the whip and coupling inside and then coat also, judging from the picture I would bet it needs cleaning also.
Then test the whip installed in the mount and report back before any trimming.
GL you're getting there and enjoy the install.
All the Best
Gary