This is one of the confusing things about collecting Sheaffer. Both of these pens are called Tuckaway, but they are two different models. There is no clear documentation on how there two models relate.
The Green pen is a model 82 SM Tuckaway and is the model shown in the "Sheaffer's 1949 Line" publication sent to dealers. It has the #8 Sheaffer nib, same as Oversize balances--the 1939-1941 Premier for example.
The Blue pen is a model 74 SM Tuckaway and, was to the best of my knowledge and belief, a 1950 or 1951 replacement. It has the #74 Sheaffer nib same as on the 1939-1941 Statesman along with many more.
Both pens are shown in a 1951 publication and both show a list price of $10.00. I do not know if both were marketed at the same time or if the 74 SW was a replacement with a smaller nib to keep Sheaffer's profit margin up. If I had to bet, the 74 SM replaced the 82 SM to keep the pen at a $10.00 price point.
I picked up a Valiant II from eBay last week. I believe it is pretty uncommon - brown striated with 14kt cap and band. It arrived this weekend and looks pretty much as described except for four cracks creaping from the corners of the clip hole. The seller described it as having "a little movement of the clip," but also "... no cracks." I certainly understand that not everybody has perfect eyesight but the cracks are very obvious to me. I have contacted the seller and am waiting to hear back and come up with a resolution.
So, on to the question... has anybody had success rebuilding the cap from one of these pens? I assume the clip and cap band are compatible with the cap from any wide-band Valiant II. If it can be done, any estimate of what it might cost me and who could do the rebuld? I'd like to have something as reference if I get the chance to negotiate with the seller. I hate to send the pen back but the cap is pretty useless in its current state.
The pen you describe seems to be the Valiant model 94W Auto in plunger vac-fill. It was available in Brown Striated and Black. The Valiant model 94T Auto lever fill was available only in black. These autographs are interesting and I have a 94W Autograph in Brown Striated with a flexible nib that is in my rotation of daily users
I switched the cap on my 94W Auto some years ago because of the same problem you have and it is a relatively straightforward procedure. However there are at least two different inner cap variations with slightly different repair techniques required. The 94W Auto and the 94W pen both have 19/32 inch cap bands with the only difference one is 14k and the other gold filled.
If you have the Model 94W Auto, the cap switch with the non-Autograph Valiant 94W requires some experience and some special tools so you do not damage the plastic, so I would suggest Rick Horne for that procedure. I do not know his price, but a major additional cost will be acquiring a donor cap. Rick can also repair the vac-fill system, if needed.
Good luck. That is a relatively uncommon pen and worth the expense of repair.