Recently I bought a 80 300td that had been sitting for a few years. It ran well. The clear filter was black, so I changed it and main filter. Then it began acting fuel starved. I couldn’t fill plastic filter pumping at loft pump. I’ve rebuilt lift pump, new primer, sent out injectors, drained tank and removed filter at bottom. It was black but not clogged greasy or crusty. Bottom of tank has some surface rust but no gunk or rusty scales. I’m not sure if I need to take tank out and clean. What do you think ？