I've seen cracks like those before.
About 15mths ago, my older neighbour complained about his 45 not dis-engaging with the cutter drive clutch handle. There was all kinds of wear on the 80s cira SB, so we tweeked a few things and replaced a few parts and still noticed the drive shaft/cutter clutch was wobbling even more than starting. Taking the motor off, we found these cracks, though they were were busy like rabbits and everywhere. Closer inspection found the previous owner had welded plate under, but had cut the plates with an oxy and didn't clean the rough slagged edges around the cut outs for the motor bolts. So tightening down the motor had compressed the rails and made the shafts not allign.
I replaced the rails (very stressful getting everything to allign perfectly)
No more cracked rails.
Just a note, if you really don't need to replace them - DON'T.
It was so blooming hard to get it perfect and I know I had a lot more LUCK than still in getting it right.
Try and find another base, if yo can't weld it!
