2000 Volkwagen Passat 2.8 Problems....Again

I’ll start from the beginning of my most recent adventure. I had just started my car and drove it approx 1/4 mile when it started screaming at me about low oil pressure at which point i immediately stopped the car and checked underneath to find a very nice collection of cracks in my oil pan. I ordered and replaced the oil pan, oil and filter and thought everything would be fine…i started the car back up and drove it the same distance with similar results. With previous problems it had missfired codes that had been corrected and so i figured i needed to clear the old codes from the computer, so i purchased a diagnostic computer to do so. I cleared the codes and tried again…not a good idea apparently. I drove back to my residence from the auto parts and supply store to hear a very unfamiliar cranking/grinding sound once i was in any higher gear than 1st and the engine had warmed up for probably 5 minutes. Now here is my question. After asking around i have had a number of different possible reasons but the most popular seemed to be a faulty oil pump. Now today i bought a pump and when speaking to the clerks at the store they told me something the others had not and that i in my inexperience did not even know was a prerequisite to using a vehicle after it was been cleared and refilled of all of its oil…priming the oil pump. I was curious if someone might be able to explain to me how this is done, if possible specifically in my make and model of vehichle…and perhaps its time to start a ‘Save the VW Owner Fund…’…or maybe just get rid of it once its operational…hmmmm