Thank you all for the replies. I knew asking the forum was the right thing.
I believe that the quickest most effecient way to determine this is to email Yamaha.
I wish it was! Prior to this I did send a mail to them but it must have caught up somewhere. I tried sending another one just in case.
After reading all the replies, I took another healthy dive into the depths and found this webpage:https://kr.yamaha.com/ko/products/contents/pianos/clavinova35th/chronicle/index.html
There's one product that's highlighted from the line-up per year. From here I browsed the year where CLP-300 was released and opened the only viewable one that was CLP-50. To my surprise, I had no idea what "ME Keyboard" actually was.
It took a hefty amount of searching, the information was so scarce that the next term I will say will probably make this thread appear in page one of the search engine for same minded searches (so hello there, fellow time travelers!). Apparently, Marshmallow Effect (ME) was a predecessor of Action Effect (AE) and one page describes it as "not as heavy as AE". Looking at the anniversary webpage, CVP-7 (1985) and (1986) CLP-50 uses this until AE was introduced in 1987 (CVP-100).
If these pictures can be trusted, it looks like an early version of the Graded Hammer (otherwise known as Graded Hammer Effect) key action:
This is surprising! I had stumbled into this website prior to making the post, but I had no idea what I was looking at! Now with extra information and using the reference webpage, and assuming the website is indeed right, I could not find a replacement key for CVP-7 (and CLP-20) however CVP-5, CVP-3, CLP-30 use the same key. Going by this logic, the entire 1985 line has these ME actions.https://syntaur.com/keyboard.php?keyboard=1151
What is confusing was CLP-50 also has the same key (and it was stated so in the product details, ME Keyboard), but CLP-300 on the same year has the same replacement keys as CLP-550 made in 1988! I am not sure if that means CLP-300 was the top of the line and thus upgraded at that time as I have no frame of reference from this.
and was phased out by the mid-1990s in favor of the "Action Effect II" keyboard, and by 2000 or a little before, the Graded Hammer Effect keyboard was introduced.
AE existed even before CLP-760, so would CLP-300 be AE1 then? Thank you for the quick piano action history too, I tried searching for manuals but found nothing.
1990: This model also featured a new AE (Action Effect) keyboard mechanism which more accurately replicated the hammer action of the acoustic piano.
At least, that is what I can take from it. There is no need to mention AE there unless there was new developments to it.
I own and still use a CLP-300 I bought new in 1986. I chose it based on the grand-like action. My own grand I loaned to a church while I was living in an apartment and needed a practice instrument to prepare for recitals. I can't tell what kind of action it has other than it is nicely weighted and has a great let-off which made it easy to transition a performance grand piano.
Another CLP-300 owner! I honestly thought it was an endangered breed.
I kept searching for other owners but posts date to a few years to a decade ago. If you do not mind the question, how are the modern Yamaha actions to you compared to the CLP-300? I took a bit of a look for your posts for some inspiration just now but I ended up seeing KX8 (GHS action if I recall) instead. The part of what you said about the action is true. However, it has been a long while since I touched any type of piano besides what I have now. Any sort of insight would be greatly appreciated.