Shock absorbers

[S.M.]

Hi everyone.
Does anyone in the group know the correct procedures for changing the hydraulic oil in the rear shock absorbers of an old motorcycle...it's not an off road motorcycle...it's a classic from the late 70s. The shock absorbers in question are from the Betor brand (Spanish) and do not contain gas, just oil. I've already disassembled it and there are two chambers where the oil circulates.....a cylinder where the piston is and another outside it. I'm also not sure how much oil is needed....
Thank you very much in advance.

[dirty_rat]

Here's an article from back in the day. Hope it helps.

[dirty_rat]

And here is another article.

[S.M.]

Thanks .....very useful article