While I understand the use of pumps when dispensing very small (1 stroke of each component)  amounts of resin and hardener I don't understand why anyone uses them when larger volumes are required.  They are both slow to use and inaccurate.  Buy yourself a digital scale on amazon and put it inside a ziplock bag to protect it from drips.  The correct MAS LV ratios by weight are 100:45 (e.g 100 grams of resin to 45 grams of hardener).  When starting a project requiring large volumes of resin I make a chart of the various volumes I think I will need so that I don't need to do the calculations on the fly.

I like this scale. https://www.amazon.com/gp/product/B0007GAWRS/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1) 

Obviously, make sure you tare the scale each time to eliminate the weight of the contain you are mixing resin in.   If you weigh your resin and hardener carefully and then mix thoroughly you will never find yourself with a batch of resin that does not harden

Pumps need air pressure to work. Try loosening the cap where it screws onto the bottle to allow incoming air to enter the bottle and equalize air pressure. The other possibility is that the replacement pump is defective.

Having a pump clog over the winter is not rare. I find replacement to be more cost-effective than cleaning. Getting a defective pump is rare, but it happens. If the internal seal is too tight, loosening the cap on the bottle can many times fix it. If the seal is too loose, sometimes repeated pumping can get it working again as the pumped material fills the gap, but in that case I wouldn't trust the accuracy.

If loosening the cap doesn't work, it's time for a new pump.

Laszlo