Here are several methuselahs that I probably discovered, although the initial states are all very similar. They're just two stairstep hexominos interacting with each other. I merely changed the distance between each other. I initially had over 20 methuselahs, but I decided to only include those that require over 1000 generations to stabilize, because that's probably a bit too much. Here are the methuselahs, from the shortest generation to the longest:
Stable pattern reached at generation 1018 with a population of 137.
x = 19, y = 4, rule = B3/S23
2.A$.2A12.2A$2A14.2A$A16.2A!
Stable pattern reached at generation 1114 with a population of 170.
x = 12, y = 4, rule = B3/S23
2.A$.2A5.2A$2A7.2A$A9.2A!
Stable pattern reached at generation 1390 with a population of 130.
x = 13, y = 4, rule = B3/S23
2.A6.2A$.2A7.2A$2A9.2A$A!
Stable pattern reached at generation 1977 with a population of 389.
x = 15, y = 5, rule = B3/S23
11.2A$2.A9.2A$.2A10.2A$2A$A!
Stable pattern reached at generation 3055 with a population of 350.
x = 19, y = 5, rule = B3/S23
15.2A$2.A13.2A$.2A14.2A$2A$A!
Stable pattern reached at generation 3379 with a population of 534.
x = 16, y = 4, rule = B3/S23
2.A$.2A9.2A$2A11.2A$A13.2A!
Stable pattern reached at generation 4326 with a population of 570.
x = 17, y = 5, rule = B3/S23
13.2A$2.A11.2A$.2A12.2A$2A$A!
I wonder if at least one of these could be anything new? I am pretty sure that there are more >1000-generation methuselahs from these two staircase hexominos, but I've used way too much of my time...