I've heard nothing but complaints from customers AND their franchise agents reegarding the quality of their 800-number service center. 

sounds like someone got a nasty gram.. we see this with the syndicators that are called out then threaten the investor who called them out.. or anyone else companing about a service only to have the company either threaten or tell them if you take this down or retract we will give you your money back.. kind of like landlords lying about how great their dead beat tenant is to just get them to move on to the next landlord. 

It may or may not show on a credit report, depends on the servicing and you should have the loan serviced.Failure to include the debt on a future loan application is mortgage fraud, wanna go to jail?

Dealing with warranty service is a pain in any situation but when you also have to deal with a tenant on top its even worse.

Are there specific lenders or servicers that are more likely to call these loans?

Welcome and thanks for your service!!

I don’t need help often but have had good luck with customer service when needed.  

Owners mistakenly ASSUME all PMCs offer the exact SAME SERVICES and PERFORM those services EXACTLY THE SAME WAY, so price is the only differentiator – so, they often select the first PMC they call or that calls them back!

Which skip trace services have you tried?

I would put it on craigslist and FB to see if anyone wants it for free.Otherwise call a junk removal or abandoned car removal service.