On the topic of substituting modern oils, I have noted periodic reports of O rings disappearing, or drying up into little chunks. Recently I was looking for design details for O rings and ran across a Parker page showing O Ring composition vs fluid compatibility. I haven't had time to study it, but it sure looked likely that seals matching old seal specs might sometimes be incompatible with synthetic oils, hydraulic or otherwise. I think it needs followed up on.
I have also read some on this, and it can come down to from what I seen, on the oils and there make up, as older parts were not made to handle many newer chemicals, plus you have to add into the equation that OLD seals and gaskets and o rings are just that OLD< and as things age they tend to get weaker, which is not helping the issues or possible ones with more modern fluids and chemicals in them!
an easy example is older fuel lines and modem ethanol fuel()yes not OIL, I know, < but a fluid) , and how it dries the hoses out(talk to anyone that works on small engines, the frustration they find on this)
modern oils also have more cleaning agents , and have different flow abilities, which is why some folks find leaks after switching to more higher end fluids over the old dino stuff!
this is why I suggested trying to stick what what worked for so long, I am not sure when this fluid you USED to use went out of production, but I am sort of guessing, it didn;t happen before maybe the last fluid was changed, so someone put something in there that I gather was working,
if your not the original owner of machine, maybe if possible talk to previous owner,
if you are the owner, when was the fluid changed last?
if things recently went out of production, I start calling dealerships to see if any have any old stock, , never know, many older dealers have a LOT of old parts sitting around,as well as fluids and such!
if not dealer, what about the world wide web, be surprised what folks hoard and then sell later on, HAHA!
a lot of farmers are famous in my area for having stock piles of fluids sitting on barns, as they seem to buy in bulk and like to have lots on hand, JUST in case!
and as they sell equipment or retire it, they SOME times have younger family members that are into selling things on line(I know a few personally that do this to there dads stashes ) trying to get rid of things taking up space they need for other things!
so finding out of production oil, might still be possible if its recently out of production if your willing to look for it
best of luck, only trying to help, no bash here meant!
