Hi,
yes, you need to download the SCA files from the marketplace and put them into the CMS inbox.
One example regarding sap_buildt:
http://service.sap.com/patches
--> Browse our Download Catalog
--> SAP NetWeaver and complementary products
--> SAP NetWeaver
--> SAP NETWEAVER 7.4
--> Entry by Component
--> Application Server Java
--> DI BUILD TOOL 7.40
--> # OS independent
--> here you find on the bottom of the page all available SPs of 740 SAPBUILDT
This note might be useful as well.
#1259604 – CMS check-in tab: Not all files from inbox are displayed
I hope this helps
Best Regards,
Ervin