Someone with a good shop vac that has a long hose can get it cleaned out pretty easily. 

Have the furnace, A/C, water heater etc all on a schedule to have inspected and serviced.

If so, new service to the building would more than likely be required independent of the existing domestic water line.

Really only things I could see that might turn off buyers is the water lines in the laundry room next to the water heater.

About a month ago I had a contractor replace a roof that got damaged from a storm but when they had the shingles off another storm blew through overnight and blew the tarp off and a lot of water got in the house.

You're treading in RESPA-infested waters there and these are federal, not state regulations.Referral fees for ANY closing services on residential loans are strictly prohibited under RESPA regulations. 

Many Martis buyers are interested in form over function and the builds can reflect that, with more $ spent on adding square footage and finishes than the details that aren't seen (insulation, ventilation, water management, etc). 

My client i funded and partnered with then went on to tell me its Clay and Clay in that area is in big demand to be used to line ponds etc as the basic soil in the area is very sandy and wont hold water..

I am debating whether i should just fix the shower pan. or, rebuild shower as well just in case water leak is coming from shower walls. what do you think? 

Water damage can cause a very serious damage to structures.Sorry I was not able to give you any specific numbers to help you but good luck, sometimes keeping it simple might be good to get started with.