Then track the date a maintenance issue was reported, description of the problem, who it was assigned to, when it's estimated to be completed, when it was completed, date/amount paid, etc.It doesn't have to be fancy.

I'd like to get $30k, I'm just not sure how to calculate the percentage of ownership that would amount to.

Your new ARV(after repair value) should be supported by an adequate amount of comparable sales in the area(duplex's).

After about 10 years I have accumulated a fair amount of small multifamily properties. 

At this point since it's after the fact while not totally correct; you may explore adding the missed asset/basis amount as a selling cost to just reduce your gain. 

(The vendors give a quote, usually discounted for being a PM client and if I approve I pay amount, no extra fees/surcharges/etc.)For this I get GREAT and immediate service.

From what you posted this is going to take a decent amount of all to make an already unprofitable property just a little less unprofitable.

I would also make sure you have a good amount set aside if something hits the fan.  

If you don’t have a certain amount of funds set aside for these situations as well as your portion of closing costs and some extra reserves for once you close then you’re likely not financially ready to be buying things.

A point is one percent (1%, 0.01) of the amount you are borrowing.