Trying to produce blanks cells for some alpha numeric charatcters and not others

I have a large spread sheet. The values in the column "O" I am referencing are M, T, numbers, and blank cells. I want to keep the T and number values in Column D, but want the M to be a blank cell and the blank cell to remain blank. The following formula does well except it is assigning both T and M as a blank cell.

=IF(COUNTIFS($o$4:$o$34,">=0",$n$4:$n$34,$A$1,$k$4:$k$34,$A4)>=1,SUMIFS($o$4:$o$34,$n$4:$n$34,$A$1,$k$4:$k$34,$A4),"")

Thanks in advance for any help that you can provide!