Hi. So, you are trying to recreate the original slide that injured you? Is this of necessity to you? My husband was a pretty serious baseball player (high school and college both) and then played softball on a competitive team more for fun. He no longer plays because he hurt his calf. Body wears out and gets old. While it bums him out, he still enjoys the sport as a spectator and coach. I don't know your age and if it is essential you still play ball and slide into base. That's for you to decide. But I personally do avoid something that causes me pain even if it didn't used to.
With that said, have you looked into Iliotibial band syndrome? My kids call it band syndrome. It's semi common with their peers in athletics (they are high school age). Lots of runners get this, for example. Pain on the outside of the knee is very often associated with it. You don't seem to have the typical cause but the pain seems a bit similar? https://www.webmd.com/pain-management/it-band-syndrome#1 And as you know have already researched, yes, that could also be a meniscus tear. you need to get that examined and sorted out though so that it doesn't become worse or more serious if this is what it is. Do you have an orthopedic doctor you can see?
How are things going? Any update on how you are doing?