I found this info on plastic plumbing that confirms what I heard and my suspicions. This info was found at http://bart.ccis.com/home/mnemeth/plumbing/plumb.htm
and copyright by Mark S. Nemeth.
Most older RV fresh water systems are plumbed using gray polybutylene tubing. Most connections are made using barbed connectors made of either gray plastic-like materials or brass and either aluminum or copper crimp rings. This plumbing will resemble the picture below. There have been a lot of claims that polybutylene plumbing breaks down and eventually leaks, usually at the connections. I spent some time researching these claims and I'm sad to say that there appears to be a pretty good case against the gray stuff. One thing is certain: they aren't making it anymore! It has been universally replaced by cross-linked polyethylene tubing in most newer RVs. Identified by it's white or red color, PEX is assumed to be safe and reliable. The connections are made either with Qest fittings or the familiar crimp rings.
While scientific evidence is scarce, it is believed that oxidants in the public water supplies, such as chlorine, react with the polybutylene piping and acetyl fittings causing them to scale and flake and become brittle. Micro fractures result, and the basic structural integrity of the system is reduced. Thus, the system becomes weak and may fail without warning causing damage to the building structure and personal property. It is believed that other factors may also contribute to the failure of polybutylene systems, such as improper installation, but it is virtually impossible to detect installation problems throughout an entire system. In most cases it takes years for polybutylene systems to fail. While it may leak within a few years of installation, the majority of leaks start to occur in the 10-15 year time frame.
Throughout the 1980's lawsuits were filed complaining of allegedly defective manufacturing and defective installation causing hundreds of millions of dollars in damages. Although the manufacturers have never admitted that poly is defective, they have agreed to fund the Class Action settlement with an initial and minimum amount of $950 million. Homeowners with houses that were plumbed with polybutylene are eligible to receive payment to replumb their homes.... unfortunately, RVs of all types were specifically excluded from the class action lawsuit settlements. The following is excerpted from the class action settlement documentation:
A "Unit" is any real property or structure situated in the United States with PB Plumbing installed between January 1, 1978 and July 31, 1995. A "Type I Unit" is a single-family residence, and each part of a commercial or other structure occupied by a single tenant or tenant group. A "Type II Unit" means a mobile home (exclusive of recreational vehicles, boats and travel trailers).
Here are a couple of web links if you want to do some research on your own:
Consumer Plumbing Recovery Center - 800-356-3496 - www.kinsella.com/polybutylene/
Spencer Class Facility - 800-490-6997 - www.spencerclass.com/
General info site for polybutylene plumbing - www.polybutylene411.org/
Poly site that references Class Action Lawsuit filed by the insurance industry against the poly resin manufacturers: - www.businessinsurance.com/mktplace/ad0308.html
Well, now that I've ruined your day, where do we go from here? One good point is that the gray stuff seems to be pretty reliable in the low water pressure environment of an RV. The other good point is that, unlike the plumbing found in houses, the plumbing in RVs is a lot more accessible. Repairs on your polybutylene piping should be done by replacing the old gray stuff with the newer PEX tubing. Qest fittings and the old style brass crimp fittings appear to be compatible with both types of tubing.