Old Yanmar

Hi, I have an old Yanmar YB-201. I'm looking for a service manual but can't find one anywhere, it's almost like the machine never existed. So my next effort is to obtain a service manual for a similar machine in the hope it will be some use to this novice.
Can a Yanmer guru assist is advising a Yanmar (or alternative brand) mini excavator which would be similar enough to the YB201 that a service manual for that machine would be useful.
Thanks in advance

Old Yanmar