Some services will be replaced by buses for the next two weekends due to engineering works.
The radio DJ says she is "utterly devastated" at the loss of two "precious" rings inside.
The radio DJ says her case went missing while she was travelling to Gloucestershire on a GWR train.
The team working on Railbus W79978 say the renovation work is likely to take a number of years.
The new Midlands hub could see 260 extra trains a week in Gloucestershire.
Rail replacement services will run from Tuesday to Saturday due to work on the track.
It took them three days to complete their challenge, which raised funds for Prospect Hospice.
The airport doubles as an aeroplane salvage yard, where retired airliners go to be disassembled.
The capsule was hidden at Kemble Railway Station in 1935 by the then station master, Cyril Feldwick.
