I had issues with our Weihrauch HW97K. I fought with it for months. I, too, didn't want to take it apart lest I void the warranty.
The reality: What I found is that a Weihrauch warranty is only as good as the vendor you bought it from. If you have any mechanical skills at all, and a little common sense, take it apart. Watch some YouTube videos about how to take it apart and reassemble it first, if you can. There are plenty on YouTube for almost everything. I think I saw some for the HW30 when I was looking for mine.
The three big things that can cause the problems you described are: 1) Bad piston seal, 2) Bad breech seal, and 3) Broken mainspring. I had all three. The mainspring wasn't immediately obvious when I looked at it, either, amazingly enough. I ordered a Vortek kit and breech seal directly from Vortak, tuned it myself, and all is much better with it now. Thank God.
Don't be afraid of it. It's not that hard.
While it's apart, I also highly recommend you give it a little tune up. Deburr and polish everything except what common sense says you shouldn't -- even things that you think shouldn't matter. Smoothen it out, anyway. Any rough spots whatsoever, no matter how slight, will potentially add more vibration. Here's a GREAT video how to do that!
As a personal touch, I also added a soft neoprene washer to each end of the spring to further reduce vibration. Vortek seemed to have neglected to include the washers that were supposed to come with it, and I didn't want to nit-pick them about it. I'm
very happy with their parts, and their service.
Then put it all back together, and chances are, it will work better, and you will be much happier and more comfortable with it since you know how it all works inside and have worked on it yourself.
Otherwise, contact the vendor you bought it from. If you contact Weihrauch, they'll just tell you to contact them. Trust me. I've been there multiple times with them with both our Weihrauch rifle and Weihrauch scope.
I hope this helps!
PS - I'd guess you have at least a blown out piston seal. If you keep shooting it with a blown out piston seal, you
*will* end up breaking the mainspring, in time. The Weihrauch piston seal in our HW97K was junk compared to the Vortek one. Even the CustomAirSeals.com piston seal looks better than the Weihrauch seal, and they're from Australia, where you are from. Feel free to DM me if you have any other questions you don't want to bother the list with. I just went through this all myself!
And be at peace. It will all work out.
PSS -- Use caution when you get to the part where the mainspring will be released, as it could have a lot of tension. If you have a 12 ft lb gun, or if your mainspring is broken, it should not be a big deal. Otherwise, it could have a good deal of pressure behind it. Don't let it get away from you. But again, a little caution is all that's necessary. And if you need a spring compressor to get it back together again, a simple woodworking clamp will do just fine.