I have 225+ kms on my 81 280zx. I just changed entirely over to sythetic. It has helped soooooo much. Better than conventional [If your Z doesn't drip at all]. Synthetics small molecules make leaks bigger. I put Mobil 1 10w30 in the engine, and Pennzoil 75w90 in the tranny and diff. Shifting improved greatly, immediatly! Plus it cleans better than conventional oil. That's my recommendation.