Oil for defender 300 tdi

Hi all,
Need some advice about engine oil for landrover defender 300tdi with 135000 on clock.my garage has put fully synthetic 5w30 oil in and since then I have a little blue smoke on start up and under heavy acceleration.turbo is fine and all breathers are clear.does anyone know if this oil is to thin for an old engine and could it be running through the valve seals.look forward to your replys.

found this

synthetic vs conventional mineral oil

The advantage of synthetic oil is that it can withstand higher temperature and can work longer without losing its lubricating qualities. It doesn't get thicker at below-zero temperatures providing good engine lubrication at a cold start. However, since it's more "thinner" a high-mileage engine filled with synthetic oil will more likely to develop leaks and you will more likely to hear lifters tapping noise at a start. Therefore, If you have low mileage or turbo engine and driving under heavy conditions such as high temperature, excessive load, long intervals without an oil change, etc., or simply want to provide extra protection for your engine, synthetic oil may be a good solution. But I don't think it's worth to use synthetic oil in high-mileage engines - thicker mineral oil will provide better protection as long as you change it regularly.

hope it helps

I have always used ther cheapest 15/40 diesel mineral oil from Asda or Morrisons. Old engines love it.

as above