While the 139 enjoys legendary status in the vintage MB community, the truly discerning curator knows that the 138 is, in fact, rarer and - in my humble opinion - more significant as a collectable star!
One key characteristic that differentiates the 138 from the 139 is the cap ring. The 138 has a single thick cap ring, while the 139 has the iconic silver rings.
This pen is from the personal collection of Stilusaurea. Read more about some beautiful vintage MBs in their collection --> link.
For bibliography, see Resources page -->link