The Bargmann 68's are an OK light fixture, but they have some problems.
First, they are prone to cracks on the colored lens. Over-tightening of the mounting screws or direct impact by just about anything will crack them. If they are full of water and freeze, that will do it, too. As JohnB mentioned, water gets into these things pretty easy so the drain holes take care of those issues.
Second, they require three holes for mounting - two screws and a larger hole for the lamp base. That's a recipe for water infiltration behind the skin. My Sunline came from the factory with a bead of caulk on the top of the fixture (but not on the sides or bottoms) on the front and rear only; just the ones up high near the roof. If I have to pull one of them off, I remove all the caulk, clean the surfaces, and the re-caulk when done.
Third, in addition to water, dirt gets into these things. Dirt acts like a sponge and holds water which ups the corrosion factor on the electric connections. So this is another good location for application of dielectric grease.
The good news is that they are fairly inexpensive - I have found them on the net for as little as $4 each. They can also be replaced with other clearance light fixtures which are readily available at auto/truck parts stores.
I am slowly replacing the 194 incandescent bulbs in mine with LED's.
'12 F250 4x4 Super Duty PowerStroke 6.7 diesel
2011 to present: '11 Cougar 326MKS
1999 to 2011: '99 Sunline T-2453
Amateur Radio kd2iat monitoring 146.52