I have seen many motors where there is pipe dope or teflon stuck in the oil pump!!

NOT All pipe threads are tapered. There is a standard for straight pipe threads, NPS. I believe the oil pickup tube is NPS.

Correct, the factory tubes and the MP replacements are straight pipe thread (measure it for yourself) but the block threads are tapered so there is enough interference fit to allow the pipe to tighten without using a jam nut.

Since a NPT combo is often known to leak, a straight/tapered combo is likely to leak also so a sealer seems prudent.

I learned something new today

I think some of you are a little confused, look at the definition of NPT. The taper is actually in the thread angle itself. Its not that the pipe (or hole) gets smaller on the end.The different thread angle is what causes the interference. This would agree with what john said above.
This is from the engineering tool box website.
the angle between the taper and the center axis of the pipe is 1o 47' 24'' (1.7899o)
truncation of roots and crests are flat
60o thread angle
pitch is measured in threads per inch

the above statement[s] are true. however, for example, a 1/4-18npt thread can be taped using a 7/16" drill for a through hole and get acceptable results. but you will get superior results using a 27/64" drill and a 1/4npt TAPERED reamer, which as the description implies, DOES make a tapered hole. this method is better because it can be used with or without sealer, and assists the 60* thread angle in doing it's job as designed. the practice of using straight through holes was started as a cost saving manufacturing move when it was discovered acceptable [usable] results could be obtained using a non tapered hole for most applications requiring pipe threads. in the above example, the 7/16" drill size is also the required size for a 1/4-18nps[coupling] thread, allowing use of just a common drill without a reamer operation for both types of pipe threads. i also own several common sizes of taper gages used to ensure the proper hole TAPER is obtained before tapping a tapered pipe thread. these gages have a very pronounced [obvious] taper that can be easily seen by the eye. i used this method daily for 42+ years as a machinist tapping 1/8 through 4"npt threads in natural gas metering devices. upon the advent of cnc machining, the tapered reamer was made obsolete in the smaller [1" or less] sizes as it was very easy to bore a tapered hole of the required dimension needed for the larger sizes, and this hole taper was a mandated check for quality purposes.