MAF query

[Quietman]

Hi - I'm new to this forum so I hope to phrase my questions clearly
I have 2 questions concerning the same car, one on here and one in electrical

I have a Peugeot 307 SW SE HDI 110 2.0 with a 52 plate
When I first bought the car it ran smoothly but there was no acceleration, I couldn't drop into 3rd and feel any sort of kick. It was checked out and the MAF was at fault. When it was replaced you could feel the effect at 2500 to 3000RPM. Last week when going up a hill there was a little falter and since then the car is back to its old pace. The air filter was changed a few weeks ago and I will change the fuel filter and have the fault codes read but it would appear that the MAF may have failed?
If it is the case, I have a couple of questions. I notice from some of the forum dialog that the advice is not to use MAFs bought on Ebay - would this be because of quality, reliability etc? I also noticed a comment indicating that it might be possible to clean it – if so how could I do it? And the last query I have is that when looking at the options, 2 numbers have come up as replacement items 5WK9621 & 5WK9623. What is the difference and would either of them do the job?
Any advice would be helpful - thanks