Is there a better (higher pressure) oil pump available for the 1.6 TD? Is low oil pressure ever a problem on these engines? I know the filter and pickup screen are clear because pressure is fine for a half hour and then only drops gradually to about 20 pounds. I am using Valvoline 5w40 diesel synthetic. I have heard that oil pressure senders can also give trouble on these cars. This problem will only get worse when the weather warms up soon.Thanks,Daniel