Seaweed & algae contain the full spectrum of organic (photo-synthetic) vitamins, all minerals and 78 natural ionic sea trace minerals, lipids, plant sterols, amino acids. Omega 3's and 6's, anti-oxidants, growth hormones, poly-phenols i.e. in short, it contains almost everything one needs to sustain life.
We recommend a Tap Wrench for tapping and driver tools. BIG-SERT OVERSIZED UNIVERSAL HEAD BOLT ENGINE BLOCK THREAD REPAIR Normally used when a helicoil or coil style insert has failed. 10 inserts of a 30mm length included in M11 & M12 kits.
Imo, what must be done is break the bond between the bolt and the head. Heating the head will expand the iron and allow the oil or wax to get in to the threads. Torching or cutting the heads off of the bolts to get the manifold off first will help. You can weld a 7/16 or 1/2 hex nut back on to make the job easier.