clockmaker.com.au In the case of a Seiko Cal 7S26, new mainsprings are lubricated with a mix of grease and graphite powder. As watch repairers have found, such mixture allows adequate lubrication for many years. Unfortunately, original Seiko S4 lubricants are not easy to source and it is very messy to apply. A good alternative is Swiss-made lubricant ***Moebius 8200 (or 8141).***
/FB_Catalog_Oils
Moebius 8200 grease is sometimes specified for mainspring barrels and is a long-time standard product in the industry, particularly for handwind watches. It can also be used as a stem and winding gear lubricant grease on many older watches. My recommendation would be to use Moebius 8141 in most applications instead. The particular application should dictate the oil.

However, at the end of the day, the point is not necessarily in the type of lubricant but how it is applied. Too much lubrication is not only unnecessary, but will cause unwanted effects to the overall performance. The trick is to apply lubrication in a very*** fine film on both sides of the mainspring***, over it's entire length and to lubricate inside the barrel wall as well.
Unlike wheels and bridges, a mainspring should NOT be cleaned with benzene or alcohol based cleaning solution. Proper cleaning consists of removal of old grease and dirt and it is best done with paper tissue or fine cloth.

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Note added at 15 hrs (2022-08-30 03:15:45 GMT)
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links,,, https://www.hodinkee.com/articles/inside-grand-seiko-evoluti... https://www.keyence.com/ss/products/microscope/vhx-casestudy... Using Clock for Watch, belt for Spring?, Japanese vocabulary using Anglicized words (belt- beruto, strap=sutorappu, spring-supuringu, clock spring, kurokkusupuringu, kurokkuberuto) https://www.watchmaterial.com/seiko-6117-6119-6138-6139-main...

https://www.keyence.com/

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Note added at 15 hrs (2022-08-30 03:20:32 GMT)
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https://www.keyence.com/about-us/ As a leading supplier of sensors, measuring systems, laser markers,*** microscopes**, and machine vision systems worldwide, KEYENCE is at the forefront of*** factory automation***. We strive to develop innovative and reliable products to meet the needs of our customers in every manufacturing industry.