Real thick sticky black wheel bearing grease probably can make it slower acting, but is petroleum based which I don't like for long term plastic exposure. The synthetic silicone is clear, clean and probably safer for storage within the dampener.
The purpose of the "slow-eject" feature is not to torture you with agonizingly slow Heinz like action but just to dampen the eject action so it doesn't slam, bam, flap and bounce during the opening process, which it WILL do without a functioning dampener. My point is that it IS possible to make it slow as molasses but I'm going to guess that the current action is closer to factory new original when the grease was still new and viscous than the ultra slow need some help type of action on examples today with the grease all dessicated. I did own an M9994 back in the day brand which I bought new and it was never a real slow door. Just silky smooth action without the BAM Smash bounce.