Its all here:
http://www.peachparts.com/Wikka/W123FuelTank
I'd recommend lining the tank with an aftermarket sealer made by POR-15:
http://www.por15.com/FUEL-TANK-REPAIR-KIT/productinfo/FTRK/. I lined the tank in my '85 with it. It's inert to both biodiesel and WVO.
(You dont need the fuel stabilizer included in this kit, thats for gas)
Trust me, it will take you less time to just pull the tank and clean it than messing with filter changes.
I'd also not recommend running your engine on high blends of WVO without using a 2 tank setup, especially as you are trying to diagnose and fix other problems. Please, no matter what blend, read up on filtering and dewatering the WVO properly.
There is no free lunch. If there's over .1% water, or worse boilout (if you don't know what this is, you need to find out) in it it will ruin your fuel system and engine very quickly.
Im no WVO hater, I run my '85 car on it. Diesel fuel is getting expensive, but if you like your car and want it to run well, use extreme caution.