I realize this is terribly late but hopefully it helps someone else with the same issue down the road. The SQL below should get you what you are looking for, as well as show you the characters for each code.
,case
when right([Lead Time Calculation],1) = char(2) then concat(left([Lead Time Calculation],len([Lead Time Calculation])-1),'D')
when right([Lead Time Calculation],1) = char(4) then concat(left([Lead Time Calculation],len([Lead Time Calculation])-1),'W')
when right([Lead Time Calculation],1) = char(5) then concat(left([Lead Time Calculation],len([Lead Time Calculation])-1),'M')
when right([Lead Time Calculation],1) = char(7) then concat(left([Lead Time Calculation],len([Lead Time Calculation])-1),'Y')
end as [Lead Time]
--
,case
when [Lead Time Calculation] is null then null
when [Lead Time Calculation] like '' then null
when right([Lead Time Calculation],1) = char(2) then cast(left([Lead Time Calculation],len([Lead Time Calculation])-1)as int)
when right([Lead Time Calculation],1) = char(4) then cast(left([Lead Time Calculation],len([Lead Time Calculation])-1)*7 as int)
when right([Lead Time Calculation],1) = char(5) then cast(left([Lead Time Calculation],len([Lead Time Calculation])-1)*30 as int)
when right([Lead Time Calculation],1) = char(7) then cast(left([Lead Time Calculation],len([Lead Time Calculation])-1)*365 as int)
end as [Lead Time Days]