Forum Member @Jani has kindly shared with myself two Recent firmwares for the DSL-N66U (many thanks) 
DSL-N66U_9.1.2.3_783-g4cb10eb.trx
DSL-N66U_v9.1.2.3_790-g61d41b5.trx
“These files have been virus checked via myself, but UKTechHub.com has not liability for these firmware’s and there usage”
DSL-N66U_9.1.2.3_783-g4cb10eb.trx –
DSL-N66U_9.1.2.3_783-g4cb10eb.trx.zip (76 downloads)
DSL-N66U_v9.1.2.3_790-g61d41b5.trx –
DSL-N66U_v9.1.2.3_790-g61d41b5.zip (192 downloads)
In a completely sane world, madness is the only freedom (J.G.Ballard).