Patrick:
I have felt your pain. However I have found the solution in the back pages of one of my many modeling references.
I dilute the Squadron green putty with Tamiya Liquid Cement inside a syringe.
I forget which article and particular magazine, but suffice to say it is over 20 years old.
In the body of the syringe I squeeze a length of squadron putty and added twice the height of the putty in liquid cement directly on top of the putty inside the syringe.
When stirred well, you can actually feel the putty "soften". I placed the plunger section into the body and squeezed out all of the excess air (hence no bubbles to find when sanding) Then I selected a syringe tip of the smallest dimension and applied the putty whereever necessary. I capped the syringe off when finished with a push pin from my noticeboard when it is not is use and the putty is still soft and applies evenly after 38 days. The best of all is that I control the amount of putty that goes out with the plunger and I can shape the tip to suit the application. Pinching the tip with a set of pliers created a nice narrow almost pencil line fine tip for weld seams on my latest kit.
I am sure you will have the same great results.
My sources for the syringes was a woodworking shop here in Ontario named LEE VALLEY that sells kits to repair loose wooden chair legs. A packet of 10 with mixed sizes of tips for $3.00 is more than enough for quite a lot of builds. I believe they do on-line ordering. Check them out some real finds there for small tools as well.
I hope this will solve your seam problem.
Cheers;
Gregory