The lower right side bolt should be a 3/8-16 X 2 1/4.
The upper 2 bolts are 3/8-16 X 2 1/2. These bolts hold the rear end in your 149 as well as the axle housing.
Information was found in the Cub Cadet parts finder :
https://www.cubcadet.com/webapp/wcs/...101&langId=-1#
The rear end will need to be removed to change the axle housing gasket. You may be able to lift frame above axle housing....for me it is easier to remove the rear end. The axle will need to be removed. Axle can be removed by removing the c-clip in the differential.
If the oil leak is coming thru the bolt hole and your 149 has the correct bolt you could try thread sealer on the bolt. Make sure the threads are clean before using thread sealer. I never tried that....not sure how well it will work.