I'm learning Japanese at an advanced age, and I'm having difficulty hearing R. Depending on the speaker, I hear one of three different consonants: R, or L but also it can sound like a D. In the first two cases, I know that it must be R, but when I mistake R for D, well, it can change the meaning. For example: I was pronouncing understood wakarimashtia as wakadimashtia because that's what I perceived. I've been replaying the lessons again and again, but I'm just not hearing it.
Is there any set of exercises or listening techniques, anything that helps? Also, is this a common problem for older students?
Addendum post comments: I see from the related post that my problem is sort of the inverse of the issue therein but nonetheless a function of my own brain literally being stuck in English. And it seems time, practice, and perseverance are my only remedies. Thank you for your time and attention.