Many years ago here in Australia a company had a compressor. For the life of me I cannot remember the name of that company at the moment, sorry.
Anyway this company used to build open compressors, from memory up to about 5 HP including domestic compressors.
Sealed units came onto the market so they then modified their open compressors, they must have put a longer shaft into them and bolted the electric motor rotor straight into the shaft. They machinated the compressor giving it a face to which the bolted a sealed tube on, which covered the rotor, sealing the gas inside.
They then bolted a electric stator over this tube, thus forming an electric motor and a semi sealed compressor.
So if the unit had a burn out you simply replaced the stator without having the gas contaminated.
I have no idea how efficient it was as I guess you would lose some efficiency having a larger gap between the rotor and the stator. and no doubt the metal tube would also influence the efficiency.
Prior to them building these semi sealed compressors they build air conditioning units. A large box with a evaporator and fan in one side and a belt driven compressor and condenser fan on the other, it was fairly primitive. The coils did not even have staggered pipes. From memory the boxes were about 7 feet x 4 feet x 4 feet and had a 5 HP compressor in them. These boxes were located outside with flow and return air ducts connected to them The ones I saw were out in the desert cooling down industrial equipment.
A lot bigger than the present day units..............