First, a light cleaning with water and ... gasp ... soap ... ain't gonna ruin a cast iron or sheet iron pan. It CLEANS the surface - as long as it is a quick and light cleaning. Nothing more. Heating it back up a bit and wiping it down with some oil/grease brings that surface right back.
Most people use some version of vegetable oil or olive oil to season their iron frypans/griddles - and to cook with. Margarine is common for frying. It takes the high heat without breaking down or scorching. So most use it.
But the best thing to use is Animal Fat - as it un-salted butter or pure lard! There's just something in the chemical make-up of animal fat that works the best.
One of the common church or community group fund raising meals around here is a Pancake and Sausage Breakfast or Supper. One of their biggest problems is with the pancakes sticking to whatever griddles people brought in to use. And even the "non-stick" ones stick. And, for those "healthy eating" reasons, they usually wipe the griddles down with margarine. About the time the really start getting people showing up, the grumbling starts because of those sticking pancakes. That's usually when some "oldtimer" will see the problem, walk over, pick up several butter patties, and throw them on the griddle. End of problem! As I said, there's just something about using un-salted butter or pure lard that works!
Growing up, my maw would fry up paw's breakfast every moring in a cast iron skillet. She only used pure lard. She'd fry his eggs in a good layer of lard. They never stuck! Any ham or bacon fried up would usually be done in another pan. The SALT in them causes burning/sticking problems. Also any SUGAR used in the curing. But sometimes when she (or us kids) would scramble some eggs and fry them in that same skillet, they would stick. Any time the surface of the skillet didn't have a little lard on it, those eggs would dry it out and stick. Now, it usually scraped off easily, but would stick a bit. Of course, those scrambled eggs were always fried firm and dry! No "snotty" scrambled eggs were allowed in our house!
So try using real UN-SALTED butter or pure lard. It may solve your problem. And you will be AMAZED at the taste!
Just my humble thoughts to share. Take them as such.
Mikey - yee ol' grumpy blacksmith out in the Hinterlands
p.s. I use cast iron at home, sheet iron when out trekking. Treated right with un-salted butter or un-salted lard, they work well for me. I just wipe them out when finished. Plus, I have a canvas bag to slip them into. It keeps gunk out of the pan, but also keeps soot from the pan getting over everything else. I only BURNED the gunk out of a pan ONCE - never again. Took far longer to re-season it than just spending the extra time scrubbing with a little salt and heat.