Found quite a bit of info on this strange machine, here's one site:
http://espee.railfan.net/spml4000.html
Apparently all scrapped by '68. It's my impression that
diesel-hydraulic requires more maintenance than diesel-electric,
and may not be as fuel-efficient. Plus, who wants an oil leak on
a locomotive? (greases the wheels)
Are there other hydraulic
locos in service now????? I dunno, but would not be surprised.
CN1's photos show the two types. I think models were sold by Riv
and OMI.