You can have the Lewmar hatches rebuilt by Select Plastics. They are the factory authorized repair facility for Lewmar:
http://www.selectplastics.com/default.htm
The ballpark price I got from them about two weeks ago for the Ocean 70 size hatch was $450-$485.
For the catch blocks you can drill out the old pop rivets and replace them. I just did that on the old Superhatch on my E30+. The progression of the "Ocean" configuration of Lewmar hatches was Superhatch (original) until somewhere in the mid 80's, Rollstop (next generation) until somewhere in the 90's and now the Ocean series.
I wouldn't use screws in place of the rivets. Eventually they will corrode as well and then you'll have to replace them with larger and larger screws.
Don't know which model you have, but the pop rivets on my hatches are 1/8" x 1/2". You don't want to try to drill all the way through with a 1/8" bit; you might damage the hole in the flange. Use a 3/16" bit and carefully drill until the head of the rivet separates from the 1/8" shaft. (Don't go too far or you will damage the catch block!) Then use a 1/8" straight punch to punch out the shaft from the inside. When replacing the rivets, the ones on the outside ends of the catch block are easier to install than the one in the middle, which is recessed in a slot. (That slot, by the way, is the "vent" position. For fully closed, the handles should latch under the bottom of the catch block. For the "vent" position the handles latch into the slot, which leaves the hatch very slightly open.)
When installing the rivets make sure you keep firm pressure on the back of the rivet tool to keep the head of the rivet seated against the catch block and the catch block firmly seated agains the flange. The nipple on the end of the rivet tool is too big to do this on the middle rivet. I had to remove the nipple and use a small hex nut and a 1/4" x 1/2" in aluminum stand-off (or spacer) to get inside the slot to keep the head of the rivet seated. (Otherwise the rivet tool will not be able to grip the shaft part of the rivet that gets pulled back to expand the rivet.) I found it easiest to install the outside rivets first, then the rivet in the slot.
You can get a hand operated pop rivet tool for about $12 and the rivets at most any hardware store.
