Identifying Duplicates based on values in another column

Hi,

I have a workbook (see attached for example) with 3000 + rows of data. The data is broken into groups via a group number in column L. In each group there should be one row of data with a 'W' in column M (ie. One winner account record per group). Each group can only have one 'W' but can have an unlimited number records with an 'L' in column M (ie. Losing account records).

I am trying to develop a formula (or multiple formulas) using conditional formatting to highlight the instances where there are:

2 or more 'W's in column M within a group (group number is in column L)
0 'W's in column M within a group (there needs to be at least one)

Is there an easy way to do this with conditional formatting?
I've tried to create this and failed many times.

Thanks in advance!

wace