You should also be collecting GL insurance certificates from those vendors and their insurance certificate should list both your PM company as well as the property owner as additional insured.

A customer purchases goods or services from a vendor.

If things break down from one property, I just call the right vendor/contractor to fix the problem and pay the cost.

Before continuing with the previous management company, I would vet them same as you would any new vendor/partner.

If the Tenant and the Landlord make arrangements for the Tenant to meet a vendor to make repairs or perform maintenance, and the Tenant fails to meet the vendor as scheduled, the Tenant shall be responsible for any charges incurred for the Tenant’s failure to meet the vendor as scheduled.

Working closely with brokers, vendors, and partners has given me access to exclusive off-market opportunities and invaluable industry knowledge that I couldn't have obtained elsewhere.

Can anyone suggest any reliable vendors?

If you can get the property manager to acknowledge their vendor did something to cause the leaks as stated by the most recent vendor you might get some assistance and it never hurts to ask, but I doubt you're getting any help with the charges after the long initial delay in reporting. 

I’m fairly confident in the actual renovation process due to my experience with facility management and vendor relations in the restaurant industry. 

Investors feel more confident hiring vendors that are investors themselves.