The broken plastic piece you described is likely the curved end cap or pivot cover located at the top roller/cassette area of the retractable shower door assembly. These small plastic end caps hold the aluminum crossbar in place and are essential for the shower curtain assembly to function correctly. For your 2021 Gulf Stream Conquest 6237LE with a 30" x 60" shower opening, identifying the exact part can be challenging without a manufacturer label or sticker on the assembly. We recommend checking the shower door frame, top rail, side rails, or inside the roller/cassette housing for any identifying labels or part numbers.

If the small end cap is not available separately, you may need to replace the entire shower screen or door assembly. However, we offer an Irvine replacement plastic shower door end cap set that fits many similar retractable shower doors. This set includes both top and bottom end caps and is priced at $19.95. You can view it here: https://elkhartrvparts.com/products/irvine-replacement-plastic-shower-door-end-cap-black

Please confirm your exact model year and finished shower opening dimensions, and send photos of any labels or the existing assembly to ensure compatibility before purchasing. This will help determine whether this replacement end cap set fits your Gulf Stream Conquest shower door or if a full assembly replacement is necessary.