Thanks for info.
I'll pull the diaphrams and look for any sign of damage.
I do see that Parts Express has replacement diaphragms "GRS RDIA1 Diaphragm for Old Version 4"x10" Midrange Horn or Similar Heppner/Foster-type Driver. Part # 280-051" at $8.90 each. Diaphram dimensions seem right, even though these horns are only 3" x 7 3/8". And these are 8 ohms.
If that doesn't fix it, oh well, not like these are rare and sought after. Been fooling aound with old console drivers for open baffles on old Magnavox 6V6 amps (8802, 175) and I liked the smaller size.