Go to
McMaster Carr's site and do a search on Loctite 5900. they sell it for US$26 for one tube.
Here's their writeup:
Loctite 5900 Silicone Flange Sealant
Loctite 5900 provides an instant seal for flanges and has superior adhesion and flexibility to accommodate joint movement. Also use on sheet metal covers, timing covers, and oil sumps. It is an RTV silicone and reaches full strength at room temperature with good resistance to oil and transmission fluid and is nonslumping, noncorrosive, and low odor. Temperature range is -65° to +400° F, begins to harden in 20 minutes, and reaches full strength in 24 hours. Supplied in a 300-ml (10.1 oz.) cartridge. Color is black. 6708A22 Each $25.67