Thanks blackmerecedes for the reply....

The temperature is around 10 degrees Celsius this time of year.
I have not been using A/C either. I'd like to achieve similar mileage as you are....450 km sounds very reasonable.

I had a compression test done approximately a year ago and the result was 174 psi on all four cylinders then. I suppose I should have one done now.

I've only ever used Liqui Moly MoS2 10w40 Synthetic oil ever since I bought it.

I haven't had any problems with oil loss for about a year and half, ever since I replaced the valve seals, but actually about 2 weeks ago I checked the oil and had to top it off...it was a little low. And this morning, I topped it off again, for the second time. There was a spot on the driveway from last night. I checked it over and it's not from the valve cover, but there is definitely a leak from somewhere, hopefully not head gasket...