U Ba Fin:
In Mahasi noting, as per the instructions described in the practical insight meditation booklet, will this practice also result in a “burning off of a stock of accumulated Sankara’s” or instead, is it the result of insight itself that leads to purification of the mind? In other words what are the mechanics of how Mahsai Method purifies the mind of mental conditioning?
Here's the key to the entire universe of meditation and psychology and yoga: when you put your awareness on something you would otherwise normally avoid, the mind's intelligence figures out how to release or "purify" the discomfort. And the body/mind will non-verbally know or have an "insight" into how to release the discomfort. Purification and insight arise together.
A longer explanation, skip to the bottom for the short answer:
If you are doing yoga and stretching the body and encounter tightness, then you simply hold the position and put your awareness on the tightness. In time, the body will realize that it is not in danger and will _slightly_ relax. So the tightness has been "purified" and the body will "know" that it can move into that extended position. There is a limit of course on what you can do in a day and consistent practice is necessary to make further progress.
If you are in psychotherapy and encounter a resistance or defensive reaction, then you simply put your attention on the thoughts and feelings of it. Other associated thougths and feelings will show up and you welcome those too. You continue to hold the sense of resisting or defensiveness in attention and eventually it becomes clear that this habit is based on something in the past, something that you now see clearly, and you are safe and can let go of that resistance, you don't need to defend yourself. So the defensive mechanism is "purified" and the mind has an "insight" into the nature of mind. Of course, there is only so much progress you can make in a day, but it can be amazing how lifelong problems can be seen through in a short time, but only if you continue therapy until you reach that goal.
If you are in meditation, using whatever meditation method, and encounter any form of dukka and hold it in awareness, then all of the above things will happen of course --- you will release body knots and psychological complexes --- but it has the potential to also include much more subtle releases related to fundamental clinging/identity. Regardless, the mechanism is the same whether by body scanning or noting or other methods: if you put your mind on ill will/dukka the natural intelligence of the mind will see the discomfort involved with clinging, aversion, or indifference and the mind itself will "release" the ill will/dukka. In meditation, progress can happen very quickly and very deeply, because it is working with the very primal aspects of clinging, aversion, or indifference which is the base of all our problems. All meditations "purify" the mind of these three poisons and give us "insights" into the nature of mind.
So many different meditation traditions and many different therapeutic methods all have the same basic core: if you put your awareness on something, the natural intelligence of the mind will try to find the least-stressful way of relating to it, whether it is in body, psychology, or deep mind.
So long story short: yes you will get the same purifications and insights using mahasi technique as goenka technique. You are completely free to use one or the other or both. Meditation techniques are all tools for helping us put our attention on things we would rather avoid and to keep us directly experiencing the ill will/dukka until the mind instinctually figures out how to release dukka.
Hope this helps in some way!