Remove Text from a String in an SSIS Package

Remove Text from a String in an SSIS Package

I am currently updating an already existing SSIS package. The current
Package pulls data from an Excel Spread Sheet that is provided by our IT
Department. It lists Machine Names of Computers and counts it for a
License Report.
I currently have the Job (derived column) strip off the M (Mobile) or D
(Desktop) from the first part of the machine name so that it returns just
the user name, which is what I need for the report.
MBRUBAKERBR => BRUBAKERBR
However, our IT Department just implemented Windows 7 and with it a new
Naming convention. Now there is a 76A, B, C or D that is added to the end
of all of the updated machines. If the machine has not been updated then
it stays with the older Naming Convention (seen Above).
There are also machines that have to stay on XP, their names have been
update to have X3A, B, C or D at the end of theirs.
MBRUBAKERBR76A or DBRUBAKERX3C
What I need is to remove the last part of the name so that I just get the
user name out of it for reporting.
The issues is I can't use a LEFT, RIGHT, LTRIM or RTRIM expression as some
of the computer names will only have the M or D in front (as they have not
yet been upgraded).
What can I do to remove these characters without rebuilding this package?