Customer has this pen

[J.Louie]

A customer of mine has this pen. It was made in London by TATEOSSIAN. It's a rollerball. The plastic threads in the cap have cracked and broken over time. It has a very sentimental value for her. I think it also has some real value too because the barrel is 92.5 silver and the cap is mother of pearl.
Does anyone have any ideas on how to fix. No kit inserts match diameter and threads. She does not want to send overseas because she's afraid she won't see it again.

 

[wade45]

Can we get a picture of the cap threads?

 

[d_bondi]

+1 on @wade45 's request.

Likely going to need to have a new cap insert machined. You will need to know the specifics of the threads (size, pitch, number of starts) and then find someone with a metal lathe that can duplicate it.