Typically its seems that the offers and counter offers go in rapid succession the same day.  

Older standard weight cast iron pipe may be wearing down after that long.

Detroit is a great place to invest so long as you understand what you are getting, all the pros and cons associated, WHERE you are investing (as detroit is a very block by block city in which values and things change very rapidly - block by block), and a solid team on the ground. 

I would be careful with self-leveler because of its weight.

A comment worth its weight in gold!

I know they are worth their weight in gold, but how did you get there?  

A good PM is worth their weight in gold.

from what we can tell there's no junior assoc waiting in the wings), and then there are three apts upstairs (2 br, 2br, 1br), all occupied.Trying to weight what seems to be one of the more favorable returns on a place that we've encountered recently, with the risk of potentially losing the main tenant in a few years and filling that space.Any thoughts?

It's not all the big furniture that costs so much, it's the ocean of little things that rapidly add up.

As you are probably aware, CA state and local laws are RAPIDLY changing and changing in favor of tenants.