I am a long time BASH sub amp user. In the past 12 years I have used 2. One died after about 8 years, and the other (now 6-7) is running fine. Both are/were the 300w units.
I also use a Dayton 500w plate amp, that has been in use for about 4 years now.
I would consider not replacing the plate amp with another plate amp though. You could remove the existing plate amp, cover the hole with a black piece of wood with binding posts on it, and run an outboard amp of your choosing. More choices for sure, and potentially better options.
I run outboard amps on both my main floor HT sub, and my big basement HT sub.
If you can find a used Crown XLS 1500 or 2000 it would be a very good sub amp. I enjoy mine full range running my Maggies, but lots of folks loving the Crown as a sub amp option. Build in digital Xover etc makes it simple to get up and running.
Good luck!