I have the same problem.
My 1990 LS400 had timing belt changed at dealer the last time. Now, after 75k miles, I have oil leak at the crankshaft. It creates a mess at the oil pan area and all the areas toward the rear of the car. I cleaned it up but it kept coming back after about 1k. It is a real mess down there.
Apparently the dealer didn't change the crankshaft seal. They did change the cam seals though.
Can the oil leak at crankshaft cause damage to the timing belt, may be in 4 to 5 years from now?
Should I have only the seal changed now? And if so, I think I'd change the timing belt too.
Or, should I just live with the mess for now and wait until the timing belt gets to its 90k-life (approx. 4 to 5 years from now) then take care of the whole thing (timing belt, water pump, coolant pipe O-ring, pulleys, tensioner, cam and crankshaft seals,...) to save the labor charge?
Thanks.