New here folks so please bare with me. Have an 89 flu419 unimog. I'm trying to replace the primary fuel filters located under the hood on the passenger side. These cannisters are on there very tight to the point im afraid im going to break something. They turn about a quarter of an inch. I opened up the nuts on the top thinking it might be a pressure issue but not much fuel came out. I than primed the system bleed and started the vehicle with the old filters in place. Any info would be greatly appreciated