new sink pump housing

I currently have a Water Ace Sink Pump (R930) ( ). The actual pump is housed in a large plastic housing (as its above ground, not sunk in a sump). This housing appears to be the same on several sink pumps from various manufacturers. On the top, there a plastic plate (used to access the filter) held down by 4 bolts (one in each corner). Two of the bolts have gotten stuck and broken the metal ring the screws go into from the plastic top of the pump housing. Now, under high pressure (washing machine draining), some water comes out the plate. as now there are only two bolts (on 1 side) that have anything to bite onto and hold the plate down tight. Two questions....
1.) Any ideas on how to reattach the metal rings to the plactic top? Or any other workaround? I have to gain access to the filter about once every month or so. I was thinking about using silicone chaulking, and reapplying each time I clean the filter. Is this doable?
2.) Can just the housing (or better yet, the top of the housing) be purchased without the pump? The pump is probably the most expensive part, and mine if just fine.
Thanks in advance.....
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