Dead Easy String Handling Question

Hi there,

I'm a bit embarrassed about this question, because I'm sure that a lot of you would find it trivial, but I'm really not the best at T-SQL and especially not string handling.

I'm trying to generate a 'parent' value, by replacing characters in the 'child' field with '---'. It's a classic Chart of Accounts sort of problem, for feeding into a Parent/Child dimension in AS. It's a lot easier to understand if you look at this:

This is the set I have:

GLCode GLDescription
0.-.-.---- Balance S
0.0.-.---- Balance S.Balance Sheet
0.0.0.---- Balance S.Balance Sheet.Balance Sheet
0.0.0.5000 Balance S.Balance Sheet.Balance Sheet.Assets - Area1
0.0.0.5001 Balance S.Balance Sheet.Balance Sheet.Assets - Area2
0.0.0.5002 Balance S.Balance Sheet.Balance Sheet.Assets - Area3

This is the set I want

Ch GLCode Par GLCode GLDescription
0.-.-.---- -.-.-.---- Balance S
0.0.-.---- 0.-.-.---- Balance S.Balance Sheet
0.0.0.---- 0.0.-.---- Balance S.Balance Sheet.Balance Sheet
0.0.0.5000 0.0.0.---- Balance S.Balance Sheet.Balance Sheet.Assets - Area1
0.0.0.5001 0.0.0.---- Balance S.Balance Sheet.Balance Sheet.Assets - Area2
0.0.0.5002 0.0.0.---- Balance S.Balance Sheet.Balance Sheet.Assets - Area3


That is to say,
0.0.0.---- is the parent of 0.0.0.5001
0.0.-.---- is the parent of 0.0.0.----
0.-.-.---- is the parent of 0.0.-.----

So, what I really need to do is replace the last non '-' string with '-'. I've tried various combos of PATINDEX, CHARINDEX, REPLACE etc, but I'm really struggling. To make in more complicated, and of the strings between the . can be any length.

Any ideas?