The HR215 is a fantastic mower. Even better when they're free. I've been a fan of the HR214 and HR215 lines for years and have rebuilt quite a few of the engines on them. A few years ago I posted a thread for a rebuild of a GXV120 I did on mylawnmowerforum.com. Rebuilding a GX140 would be pretty much the same. Here's the link to that thread.
https://www.mylawnmowerforum.com/fo...air-discussion/8313-honda-gxv120-rebuild.html
Your full model number is most likely HR215SXA-K1, which translates to:
HR - Honda Rotary
21 - 21" cutting deck
5 - GXV140 engine
S - Gear drive transmission
X - Recoil start
A - USA market
The K1 is a designation of a design change. In the case of the Masters it would be such things as the engine shroud, air cleaner and the color of the deck and handle bars was different than the earlier HR215. Maybe a few other things than I'm forgetting, but mostly cosmetic.
A really great place to find parts for your Honda is boats.net. In fact, my preferred Honda dealer retired recently and now does work our of his home garage. He uses boats.net to get the parts he needs.
Just go to their Honda section, choose Lawnmower parts, then scroll down the list until you get to the HR215s.
The nice thing about it is that when you choose a part from the parts list, you can then find all the other models that part will fit by scrolling down the page.. Actually, many of the HR215 deck parts were used throughout the model line, the HR214 before it and the HR216.