I've often wondered about MLS. Ever since we picked up our company S-76B from maintenance and found shortly afterwards that some "helpful" avionics engineer had been fiddling and had changed the ILS receiver frequencies to MLS. We found out in solid IMC whilst being vectored for the ILS. We had no idea this was possible and had no idea how it had been done, or how to change it back again. That caused a few more grey hairs.