You'll find a lot of multis built in the late 1890s to the 1930s and those come with all the usual physical plant precautions - knob & tube, cedar pilings, ancient plumbing, etc.RPR is a good tool, but more than that, I'd be looking at Trulia's crime heat maps and MLS rental histories. 

What I love about them the most is that the hosts always have the beginner investors in mind, so it doesn't sound like ancient Greek to newbies.

Has ancient HVAC system (that would be replaced at a later date), interiors are good (enough for renters).

I had my email hacked a few ago and it mailed stuff to everyone including BPers, telling them I had a sick relative in Greece and needed money!

Contemplating oil to gas conversion of four ancient oil boilers in a 4-plex where leases stipulate that new tenants receive their tanks 'full' must have auto-delivery contract and leave tank full upon lease expiration.

Find some ancient cottages and start mail-blasting the owners.

I just finished with "The Richest Man in Babylon" which I would highly recommend to listen to in the car if you can get past all the ancient names!

There is some hideous vinyl in the kitchen & dining and the water heater is ancient, but the HVAC is brand new.

This was in 2007 and the country I left was Greece.

These ancient furnaces aren't as energy efficient as today's models, and you don't want one to give out right away.b) Make sure that the furnace filters are changed on a regular basis.