I uploaded a form I call Bamboo Long-billed Gnatwren to the list. Birds of Peru mentions ssp obscurus from dry mid Huallaga Valley from Santa Rosa (Ucayali) S to Junin - that has white tail spots - and then says "also is southern Ucayali and Madre de Dios, where may be more prevalent in bamboo"!
This does not sound right. How can the same form both be in dry valleys in Central Peru and humid rainforest in bamboo? Unless, it is one of those dry forest/bamboo specialists that do seasonal movements. The song described for oscurus fits perfectly what I recorded in the bamboo at Amigos last year.
Shall try to get recordings from Central Peru to compare. In any case the form seems different enough and species status is highly suspected.