Do not run synthetic oil in an engine using leaded gasoline. Synthetics do a poor job of keeping the lead residues (from blow-by gases) in suspension. It precipitates out as a sludge which will ultimately damage your engine. Mineral-based oils work better in this respect.
Exxon discovered this problem a decade ago when they marketed a synthetic aviation oil for general aviation, piston engine planes. Whatever they sell in Senegal probably has less lead than 100LL avgas, but some modern car engines are sensitive to sludging as it is.
Why should Senegal have leaded gasoline? Do you know of any cars which DON"T require unleaded gasoline, being sold anywhere in the world? Unless, you do, and Senegal has only leaded gasoline, this seems to be a solution without a problem.