I agree, but today's world of made in China cheap and break products your sometimes forced to take added steps. First you need to get it handled under warranty, this well tell you who can then tell us how good their customer service is. If you continue to have problems with the new light then I would personally, and I've done this, e-mail the company and explain your issue and give them ideas on how to correct the problem; and tell them that cyclists do belong to forums where bad and good products are discussed, and by them making a poor quality product that it for one will prevent you from buying their brand again; and for two, that information is shared with other riders; and for three most online retailers have reviews of products and negative reviews will effect their profits.

They may or may not care, that's not your decision, but eventually bad products get talked about and companies will eventually lose market shares if your problem is not a fluke. And speaking of reviews, if the replacement light is not satisfactory and/or the customer service is bad or slow, then you need to do some reviews and warn others; equally if the company quickly solves the problem and the replacement light is satisfactory then you need to do a review for a positive rating. If you can spend time on a forum then you can spend time doing positive and/or negative reviews for others to read.

If you get the replacement light and rain still gets in then get it replaced again and tell them it's not sealed against water and give them ideas on how to fix it. But I would bug them and keep sending the damn thing back until the warranty period expires then I would do the thin silicone trick.