Ralph, the MS transmission design follows closely to that of the 280 I/O transmission. Many of these parts will interchange.
You may try pulling it apart, and very carefully lap the sliding sleeve into each gear cup.
The sleeve is directional, so be sure to lap like for like.
Look closely at the vertical shaft split ring keeper.... aka wear washer.
Any expansion of this ring can lead to failure and to severe damage.
The OEM will not cover the lapping, as there is no OEM recommendation for this.
There is a procedure for when lapping that seems to work well.
Get hold of me if you need help.