At 76000 miles the engine is probably getting worn enough to make it not worth while replacing the crankshaft oil seal (behind the clutch & flywheel). Probably best to just check the oil level regularly - like every time you fill with petrol (you should be doing this anyway). Keep the oil topped-up correctly and you'll be okay. Also, the engine will always be getting a little new oil into its system, which is no bad thing. You can get an oil additive which is reputed to be able to make slightly-leaking seal swell a little. Worth trying - might cure it for a while.