Hydraulic trim pumps question
 

I need some advice because of hydraulic pump units.

I must replace both hydraulic tilt trim pumps for the Mercruiser Bravo 2 stern drives. The reason is that both pumps were stolen from the boat in the marina I kept it at that time. Wanting to replace both pumps I have been looking around on Ebay for used or second hand pumps. Original pumps are expensive and as I have to do several other repairs on the boat I was thinking maybe used pumps could be all right for a number of years. The original parts number of these pumps is 865380A25 Pump Assy Trim. The reason why I prefer second hand parts is the price of the two new pump units is about one thousand US dollars for each unit where I live. I can get much cheaper things, aftermarket knock-offs from China, for much less, like a third of the price of a new one, or a used pump unit for something like a hundred US dollars.


My question is this: Is it a good idea to buy used pumps units, or a knock-off, to save money?
How long are hydraulic trim-tilt pumps supposed to last, in term of years and average usage?

I would also like to ask, in case the pumps fail, what can go wrong with them and can they be repaired? Thanks for any replies.