There is a book called "The Secret Language of Your Body" by Inna Segal. It's more detailed than Louise Hay's "You Can Heal Your Life". It might give you some more insights into your health issue.

Here is what it says about growths.

"Growths - Supression, stuck emotions, frozen tears. Pushing away, rather than dealing with, problems. Hiding, covering up, burying old dreams. Feeling unfulfilled, unsatisfied, disappointed. Carrying guilt and resentment. Holding on to past failures."

You said

"I am definitely not nursing any old hurts any more."

Sometimes our issues feel so familiar to us that we tend to easily dismiss the obvious.

Your previous answer from this thread might also give you some more specific insights into this, especially the following sentence.

"In at least two occasions in the past I have done something stupid, in moments of blind rage. Since then I have been waiting for the Universe to give me an opportunity to remedy them. Still waiting."

But of course, it is not helpful to know what the problem is when you don't know how to solve it. So here is what I would do.

1. I would take "at least" these "two occasions" from the past and completely clear them using some clearing technique like EFT.
2. I would really go deep into these specific memories and not just tap on them superficially (which most people tend to do). Learning about the standard EFT and the definition of specific events as told by Gairy Craig can be very helpful.
3. While tapping on these events, other memories with similar emotions in them might come up. Write them down and tap on them later.

Once you clear all those negative vibrations underlying your health issue, it might resolve on itself. Or you might feel positively inspired to do something to solve it.

As a side note: If you can't clear those memories yourself for whatever reason, it might be helpful get help from a healer/practitioner of any healing technique that you believe in.

"I laugh it all away every other year, but this time I thought, well, I've given it 4.5 years and it still hasn't shifted, so it's probably time to give up on it and have the damn thing operated, even though I stay well away from modern medicine."

The best way I know is get to the root cause (specific memories) of any issue and to then take inspired action. However, the second best approach is to take action through the past of least resistance without clearing the underlying issue.

Because you say that you regularly visit institutions of modern medicine (i.e. checkups), it tells me that your belief system is manifesting these visits and therefore believing in them to some degree. So it seems very probable to me that it could be the path of least resistance for you (right now) to just go to there and have your issue solved as they are suggesting.