I use straight SAE 30 weight. I live in the south and only run my machine in the summer.
Sears and Craftsman both provide service for their riding lawnmowers,For parts you can go to SearsPartsDirect.com on the internet
Check your shear pins.
The 20HP Mercury outboard with serial number 9137627 was made in 1979.
From everything I see the 125 is a 42" mower with a 20HP engine. The STX-38 mowers were 38" with either a 12.5 or a 13HP engine. So, yes the 125 is bigger than the STX-38.
That would be 20hp
1978
96
Depends on what engine you have.
your motor is a 1975 200 20hp you can get more info here: http://www.autorepairmanuals.biz/site/573683/page/599300
50 to 1
Depends on what engine you have.
Yes, remote steering kits were manufactured for the 20hp by Mercury Marine. Availability and part number can be found by serial number of the engine.