Brass HO diesel locos... Upgrade or sell? - Model Railroader Magazine

70humdinger,
It all depends on the brass importer.  What brass diesel brands do you have?  Alco, Oriental, PFM, NJ/Custom Brass, Overland, Precision Scale, Tenshodo...  All have different expectations based on the importer and the era they were made in.

I have a number of brass diesels, one of this is the old Alco Models brass RS-1.  I'm never putting a DCC decoder in it because I have much better Atlas RS-1's.  The Alco Models RS-1 is noisy and only has 4-wheel pick up.  Meh, I'll pass.  My more modern Overlands all have DCC.

The difficulties in converting brass engines to DCC is mostly overblown.  It's usually easier than an Athearn blue box.