wow- only 3 months new~
since a system is only as robust as the weakest link....the aluminum mod may then wear the edge(s) of the safety belt fabric (unless) smooth contact is made
....maybe some sort of adjustment to the retractor/ seat belt track positioning is in order? I can only imagine that MB engineers would have factored-out this type premature failure possibility in the base design...
maybe an entire custom made aluminum arm/presenter will remedy the situation for good? ...if you do happen to make one, you can sell them here like guido does with his piggy tails!
good luck, and let us know what turns out