There is no need to go back to old old old old old oleg Fimware.
The Enthusiast-Fimware features both kernels 2.4 and 2.6. Just use WL500gp-1.9.2.7-d-r2624 (d-Branch is kernel 2.4) if you have issues with the rtn-Branch (kernel 2.6).
lly and theMiron did a great job enhancing the last oleg. They fixed many security issues and improved stability.
RT-N66U TomatoUSB 1.28.0000 MIPSR2-135 K26AC USB AIO-64K running Entware-NG
pyload 0.4.9
minidlna 1.1.2
samba 3.6.5
openvpn 2.3.10
̶W̶L̶5̶0̶0̶g̶P̶ ̶1̶.̶9̶.̶2̶.̶7̶-̶r̶t̶n̶-̶r̶4̶7̶5̶0 retired