The crystallographic and magnetic properties of the solution grown RMn2+xAl10−x (R=Gd and La) crystals with tetragonal (P4∕nmm) structure are investigated. For these, single-crystal x-ray diffraction results have shown the preferential occupation of excess manganese on the aluminum 8i crystallographic site. Due to excess Mn, there is evidence of local-moment magnetism in LaMn2+xAl10−x and their random distribution is thought to be responsible for the magnetic correlations below ∼50K and the spin-glass behavior below ∼3K. For GdMn2+xAl10−x, the extra manganese influences temperature below which the sample enters into a state with a net ferromagnetic component: TC≈16K for GdMn2.21(4)Al9.79(4) and 25.5K for GdMn2.39(2)Al9.61(2). Assuming a linear dependence between TC and excess Mn concentration, the fully stoichiometric and ordered GdMn2Al10 should have TC≈5K.