Sorry, Robt, but it doesn't work that way.

When two objects collide, they must do so NO SLOWER than the escape velocity of one relative to the other (remember, escape velocity is a scalar, not vector, quantity). If you approach your target at any speed, you fall towards it gaining even more speed, (relative to the target)regardless of the angle of approach. In the slingshot maneuver, the smaller object leaves the encounter faster than it approached (that's the whole point). Momentum and energy of the entire system are conserved, of course, by the planet slowing down by a miniscule amount. This is transferred to the spacecraft, but there is no contact. Planetary accretion always involves a lot of fireworks, the planetesimals convert energy of motion to heat, that's why there is so much evidence of massive lava flows on the moon. That comes from the gravitational energy lost by the collision.

The gravitational interaction of two approaching bodies offers only a limited number of alternatives. As they fall towards each other, the gravitational potential energy is converted to kinetic energy. They will then either collide inelastically (a lot of the kinetic energy is converted to heat)or they will swing around each other (if there is any lateral vector of velocity) and go slingshotting in opposite directions at speeds inversely proportional to their masses.
(If one body is much more massive than the other its peturbation may not be noticeable, as in the spacecraft example, but it is there, Newton demands it. There is no "glancing blow" although large amounts of debris may be ejected into orbit, as we suspect may have formed our own moon.

What you never get as a result of such an interaction is a mutual orbiting of two intact bodies. That must be done by adding or subtracting excess energy (aerodynamic braking, a powered rocket burn, or other masses nearby to provide or drain off excess energy and momentum. The latter is dynamically possible (its how you get ejections) but its very rare, things have to line up just right.

To put it another way, place two isolated stationary masses a large distance apart, and mutual gravitation will cause them to eventually collide at escape velocity. And that will not be the gentle kiss of snooker balls, it will be catastrophic.