We are often asked about line boring a case, be clear that line boring does not recondition the case, it only patches it up to go a few more miles. Every line bored case we tested suffered from low oil pressure when hot (with the stock pump), often within as little as 1000 miles. That is the reason people sell huge oversize oil pumps, booster springs and longer relief valves. If the case was properly reconditioned it could use the stock VW pump, relief valves, springs and have normal oil pressure at idle when hot just like it did when new.
When VW reconditioned cases (up until 1968) they did far more than just line bore. To properly recondition a case today consists of; cleaning the case, bolting it together with an alignment bar in the crank and cam tunnel, torquing to stress relief specifications. Have the case stress relieved for 3-1/2 hours and let cool in the oven. When cool, take it out of the oven and re-torque to stress relief specifications and again stress relief for 3-1/2 hours. When cool remove from the oven and disassemble, remove all of the studs and alignment pins, machine both halves of the case flat and reinstall all of the studs and pins and torque to running torque specifications. Now, line bore the crank, and cam tunnel, often back to standard, bore the oil pump, pulley, flywheel seal holes and the cam seal groove. Lastly, the brass drive gear must be cut smaller on the OD the same amount that the 3 and 4 side of the case was machined.
After all this work and expense (far more than a new case costs) you have a case that will only provide 70% to 80% of the life that a new one will (and that's when used for stock applications). The life would be far less with a performance engine. Obviously, VW stopped reconditioning cases in 1968 due to the cost in relationship to the cost of a new case, plus now being assured of 100% of the engine's life, especially if used for higher performance applications. VW could melt the old case, cast a new case and machine it in the new automatic machinery far cheaper.