Try creating a formula like this and then grouping on it:
Left({MyTable.MyField}, 9)
If there are some records where you need to look for the L and don't want to strip off the last character if the L isn't there, you could use a formula like this:
if InStr({MyTable.MyField}, 'L') = Length({MyTable.MyField}) - 1 then
Left({MyTable.MyField}, Length({MyTable.MyField}) - 1)
else
{MyTable.MyField}
-Dell