The $40 TSC UTF is the cheapest I would (do) run in a Powershift, I think its formulated to reduce foaming and is multigrade. But TSC, Autozone, etc also have 'Yellow Bucket' cheap $25 UTF claimed to be a suitable equivalent to what was used back when these tractors were built. I think it's single weight, not multigrade.
I wouldn't use Yellow Bucket as the long term refill for a powershift. But for a manual transmission tractor only used for puttering around I think its sufficient. I used it for years in the YM240 and put the remainder of the 5 gallons in my (1980's) 3-point backhoe that also specifies UTF.
But the problem with buying this junk oil for a flush, perhaps thinned with diesel, is you will have a couple of gallons unused left over in the bucket. I tried adding it 32:1 as engine fuel. That ran fine but it smells bad like an overheated transmission.
I wouldn't run flushed oil as fuel. There could be microscopic metal debris to cause extreme wear in the injector pump. Take it in where you take used motor oil.
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If you want to start the engine for only a moment without turning the transmission just have somebody hold the clutch pedal down!