LINQ Query - Left Join Question

Hello all,

From my attached LINQ query I have here, I am having trouble where I only want to LEFT JOIN the CUSTGRP table to the CUST table so I can use in my where condition a field from the CUSTGRP table as shown.  How do I do this where I only return the DISTINCT CUST records but can filter out those based on the cust group filter I pass into it?  

I pass two param strings as you can see which one of them I filter the CUST table and the second I need to filter the CUSTGRP table so only I only pull the Customer records that have that condition and I join the two tables on CUSTID.  Again I only want the distinct records though from CUST only for the return results.

Hopefully this makes sense.  I tried messing around with the DefaultIfEmpty() but was always getting duplicate rows from CUST.

Thanks

public List<Customer> GetCustByName(string custRegionFragment, string grpFragment) {
            List<Customer> cf = new List<Customer>();

            using (CC = new CustModelEntities()) {
                    cf = (from CUST in CC.Customers
                          join CUSTGRP in CC.CustGroup on
                          CUST.CustId equals CUSTGRP.CustId
                             where CUST.CUSTLOC != null &&
                              (string.IsNullOrEmpty(custRegionFragment) ||
                               CUST.CUSTREGION.ToUpper().Contains(custRegionFragment.ToUpper())) &&
                              (string.IsNullOrEmpty(grpFragment) ||
                               CUSTGRP.GROUP.ToUpper().Contains(grpFragment.ToUpper()))
                            select CUST).ToList();
            }
           
            return cf;
        }

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