Re: 2003 Johnson 50HP Power Trim/Tilt Assembly
If your boat doesn't nose into the waves then I can't think of any reason operating w/o trim would be considered unsafe. It takes longer to get on plane, top speed is less, gas consumption is more, ride can be rougher, trailering can be a pain, etc. etc.
It is a little young to be having problems with your Manual Release Valve. If you use the MRV a lot and make it extra tight then the rubber tip or seat can wear out. When everything is perfect, you can actually feel the rubber tip make contact and just a small 1/10th turn gives you a solid seal. If you overtighten then the steel body can dig into the aluminum base and cut grooves. But since you put question marks after it then I assume you don't use it much and it shouldn't have any reason to be worn.
That would put the problem squarely back onto check valves. It is not such a good design. They used a new "miracle plastic" that could replace metal in certain situations. Same delrin type stuff they use to make plastic gears. But they did not design it with any orings. Orings work when compressed ffrom 10-20%. This means a system with orings does not have to have two perfectly round surfaces that exactly match. The rubber squeezes into shape like a gasket. It's meant to do that. The OMC design does not have any such give. The hydraulic pressure has to jam the plastic into a tapered hole with enough force to squash it into shape. During use, the poppet will rotate since it is basically a free floating piston. As it rotates the plastic is pushed and pulled at different stress points. It is not as good a design as other models and nobody has used the same technique before or since. It is not uncommon to see failures. In fact, failures are common enough that OMC ran out of inventory and no longer has any replacements to sell. As such, I would bet dollars to donuts that your check valves need replacing.
Rebuild Kit Evinrude Johnson Trim Tilt 25 35 40 48 50 HP 1989 2004 435567 | eBay