It is against common knowledge but I like silicone oils in all my air guns, including this one, and my questionable HW30 which definitely gained power. This Diana also feels better.
Good grief. You came on here and asked for advice because you didn’t know what you had. Mike Driskill gave you the best advice of all. Stop shooting it until you have the correct seals. And then when they’re replaced the GISS system has to be put back together and shimmed and timed perfectly or the gun will wreck itself. There are many parts for these guns that are no longer available. I’d send it out. If not, then at least get the correct seals and a copy of the factory manual which will give you the exact measurements and detailed instructions on rebuild. I read the manual for my 75 and said, “Airgunwerks it is”!